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CBSE Class 12 Board Exam 2023 : Physics

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Supriya Singh
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( ) KENDRIYA VIDYALAYA SANGATHAN (JAMMU REGION) SAMPLE PAPER FOR CLASS XII PHYSICS (042) , , , -180004 Regional Office, Jammu, Near Govt. Hospital, Gandhi Nagar, Jammu-180004 KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -1 CLASS : XII SUBJECT: PHYSICS TIME: 3 hrs M.M: 70 General Instructions: (1) There are 35 questions in all. All questions are compulsory (2) This question paper has five sections: Section A, Section B, Section C, Section D andSection E. All the sections are compulsory. (3) Section A contains eighteen MCQ of 1 mark each, Section B contains seven questionsof two marks each, Section C contains five questions of three marks each, section D contains three long questions of five marks each and Section E contains two case study based questions of 4 marks each. (4) There is no overall choice. However, an internal choice has been provided in section B, C, D and E. You have to attempt only one of the choices in such questions. 5. Use of calculators is not allowed. SECTION A Q. NO. 1 MARK S The electrostatic potential on the perpendicular bisector due to an electric dipole is _____________. 1 (i) Zero (ii) 1 (iii) Infinite (iv) Negative 2 Consider a uniform electric field in the z-direction. The potential is a constant (i) for any x for a given z (ii) for any y for a given z (iii) on the x-y plane for a given z (iv) all of these 1 3 4 The temperature (T) dependence of resistivity of materials A andmaterial B is represented by fig (i) and fig (ii) respectively. Identify material A and material B. (i) material A is copper and material B is germanium (ii) material A is germanium and material B is copper (iii) material A is nichrome and material B is germanium (iv) material A is copper and material B is nichrome The magnetic moment of a current I carrying a circular coil of radius r and number of turns N varies as (i) (ii) (iii) (iv) 1 1 r4 r2 1/r4 R 5 Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field B = B0k. (i) They have equal z-components of momenta. (ii) They must have equal charges. (iii) They necessarily represent a particle- antiparticle pair. (iv) The charge to mass ratio satisfy: (e/m)1+(e/m)2=0 1 6 Which of the following has higher magnetic susceptibility? 1 (i) (ii) (iii) (iv) Diamagnetic Paramagnetic Superparamagnetic Ferromagnetic 7 An induced e.m.f. is produced when a magnet is plunged into a coil. The strength of the induced e.m.f. is independent of 1 (i) the strength of the magnet (ii) number of turns of coil (iii) the resistivity of the wire of the coil (iv) speed with which the magnet is moved 8 9 Which of the following has maximum penetrating power? (i) Ultraviolet radiation (ii) Microwaves (iii) -rays (iv) Radio waves The polarity of induced emf is given by (i) (ii) (iii) (iv) Ampere s circuital law Biot-Savart law Lenz s law Fleming s right hand rule 1 1 10 What is the geometric shape of the wavefront that originates when a plane wave passes through a convex lens? (i) Converging spherical (ii) Diverging spherical (iii) Plane (iv) None of the above 1 11 Kinetic energy of emitted electrons depends upon (i) frequency (ii) intensity (iii) nature of atmosphere surrounding the electrons (iv) none of these 1 12 The radius of the innermost electron orbit of a hydrogen atom is5.3 10 11 m. The radius of the n =3 orbit is 1 (i) 1.01 x 10-10m (ii) 1.59 X 10-10m (iii) 2.12 x 10-10m (iv) 4.77 X 10-10m 13 When the number of nucleons in nuclei increases, the binding energy per nucleon 1 . (i) increases continuously with mass number (ii) decreases continuously with mass number (iii) remains constant with mass number (iv) first increases and then decreases with increase of mass number. 14 What is the resistivity of a pure semiconductor at absolute zero ? 1 15 (i) Zero (ii) Infinity (iii) Same as that of conductors at room temperature (iv) Same as that of insulators at room temperature The electric potential V as a function of distance X is shown in thefigure. 1 The graph of the magnitude of electric field intensity E as afunction of X is 16 (i) (ii) (iii) (iv) Two statements are given-one labelled Assertion (A) and the otherlabelled 1 Reason (R). Select the correct answer to these questionsfrom the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true and R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is also false ASSERTION(A): A pure semiconductor has negative temperature coefficient of resistance. REASON: In a semiconductor on raising the temperature, more charge carriers are released, conductance increases and resistance decreases. 17 Two statements are given-one labelled Assertion (A) and the other labelled 1 Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true and R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is also false ASSERTION: Thin film such as soap bubble or a thin layer of oil on water show beautiful colours when illuminated by white light. REASON: It happens due to the interference of light reflected from upper and lower face of the thin film. 18 Two statements are given-one labelled Assertion (A) and the other labelled 1 Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b Both A and R are true and R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is also false Assertion(A) : In process of photoelectric emission, all emitted electrons do not have same kinetic energy. Reason(R) : If radiation falling on photosensitive surface of a metal consists of different wavelength then energy acquired by electrons absorbing photons of different wavelengths shall be different. SECTION B 19 20 21 Welders wear special goggles or face masks with glass windows to protect their eyes from electromagnetic radiations. Name the radiations and write the range of their frequency. In what way is the behaviour of a diamagnetic material different from that of a paramagnetic, when kept in an external magnetic field? Write any two characteristic properties of nuclear force. 2 2 2 OR If both the number of protons and neutrons in a nuclear reaction is conserved, in what way is mass converted into energy (or vice versa)? Explain giving one example. 22 How does the angle of minimum deviation of a glass prism vary, if the incident violet light is replaced with red light? 2 23 24 25 Draw energy band diagram for p type semiconductor. Mark its acceptor level 2 also OR Explain how a depletion region is formed in a junction diode. How does the fringe width of interference fringes change, when the whole apparatus of Young s experiment is kept in a liquid of refractive index 1.3? Two small identical electrical dipoles AB and CD, each of dipole moment p are kept at an angle of 120 as shown in the figure. What is the resultant dipole moment of this combination? If this system is subjected to the electric field (E) directed along +X direction, what will be the magnitude and direction of the torque acting on this? 2 SECTION C 26 (a)Show how a moving coil galvanometer can be converted into an ammeter. 3 (b) A galvanometer has a resistance 30 and gives a full-scale deflection for a current of 2mA. How much resistance in what way must be connected to convert into an ammeter of range 0.3A? 27. How is the mutual inductance of a pair of coils affected when 3 (a) Separation between the coils is increased. (b) The number of turns of each coil is increased (c) A thin iron sheet is placed between two coils, other factors remaining the same. Explain the answer in each case. 28 Draw the phasor diagram of a series LCR connected across an ac source V= Vo 3 sin t. Hence, derive the expression for the impedance of the circuit. OR A lamp is connected in series with a capacitor. Predict your observation when this combination is connected in turn across (i) ac source and (ii) a dc battery. What change would you notice in each case if the capacitance of the capacitor is increased? 29 Plot a graph showing the variation of stopping potential with the frequency of incident radiation for two different photosensitive materials having work functions W1 and W2 (W1 > W2). On what factors does the (i) slope and (ii) intercept of the lines depend?. 3 . OR A proton and a deuteron are accelerated through the same accelerating potential. Which one of the two has (a) greater value of de-Broglie wavelength associated with it, and (b) less momentum? Give reasons to justify your answer 30 Define the terms (i) cut-off voltage and (ii) threshold frequency in relation 3 to the phenomenon of photoelectric effect. Using Einstein s photoelectric equation show how the cut-off voltage and threshold frequency for a given photosensitive material can be determined with the help of a suitable plot/graph. SECTION D 31 (a) Write two properties of equipotential surfaces. Depict equipotential 5 surfaces due to an isolated point charge. Why do the equipotential surfaces get closer as the distance between the equipotential surface and the source charge decreases? (b) An electric dipole of dipole moment p, is placed in a uniform electric field E ,. Deduce the expression for the torque x acting on it. Or (a) Derive an expression of capacitance for a parallel plate capacitor. (b) A parallel plate capacitor of capacitance C is charged to a potential V by a battery. Without disconnecting the battery, the distance between the plates is tripled and a dielectric medium of k = 10 is introduced between the plates is tripled and a dielectric medium of k = 10 is introduced between the plates of the capacitor. Explain giving reasons, how will the following be affected: (i) capacitance of the capacitor (ii) charge on the capacitor. 32 . 5 (a) Two cells of emfs E1 and E2 and internal resistances 1and 2 respectively are connected in parallel as shown in the figure. Deduce the expression for the (i) equivalent emf of the combination (ii) equivalent internal resistance of the combination OR (a) State the two Kirchhoff s rules used in the analysis of electric circuits and explain them. (b) Derive the equation of the balanced state in a Wheatstone bridge using Kirchhoff s laws. 33 a) Draw a neat labelled ray diagram of a compound microscope. 5 Explain briefly its working. b) Why must both the objective and the eye-piece of a compound microscope have short focal lengths? OR a) Write two points of difference between an interference pattern and a diffraction pattern. b) (i) A ray of light incident on face AB of an equilateral glass prism, shows minimum deviation of 30 . Calculate the speed of light through the prism. (ii) Find the angle of incidence at face AB so that the emergent ray grazes along the face AC. SECTION E 34 Case Study : Read the following paragraph and answer the questions. A compound microscope consist of two lenses . A lens of short aperture and short focal length facing the object is called the object lens and another lens of short focal length but large aperture is called the eye lens . Magnifying power is defined as the ration of angle subtended by the final image at the eye to the angle subtended by the object is seen directly, when both are placed at least distance of distinct vision . 1. What would be the aperture & focal length of objective of a compound microscope? 2. Why compound microscope is preferred over simple microscope? 3. A compound microscope with an objective of 1.0 cm , focal length and eyepiece 2.0 cm . Focal length of a tube is 20 cm . Calculate the magnifying power of the microscope 4. What is the nature of final image formed by Final image formed by compound microscope 35 Case study: Formation of pn junction Read the following paragraph and answer the questions Consider a thin p-type silicon (p-Si) semiconductor wafer. By adding precisely a small quantity of pentavelent impurity, part of the p-Si wafer can be converted into n-Si. There are several processes by which a semiconductor can be formed. The wafer now contains p-region and n-region and a metallurgical junction between p-, and n- region. Two important processes occur during the formation of a p-n junction: diffusion and drift. We know that in an n-type semiconductor, the concentration of electrons (number of electrons per unit volume) is more compared to the concentration of holes. Similarly, in a p-type semiconductor, the concentration of holes is more than the concentration of electrons. During the formation of p-n junction, and due to the concentration gradient across p-, and n- sides, holes diffuse from p-side to n-side (p n) and electrons diffuse from nside to p-side (n p). This motion of charge carries gives rise to diffusion current across the junction. 1. How can a p-type semiconductor be converted into n- type semiconductor? 2. Name the two processes used in formation of pn junction. 3. What are minority charge carriers in p type semiconductor. 4. Why diffusion occurs during formation of pn junction? KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -2 CLASS : XII SUBJECT: PHYSICS TIME: 3 hrs M.M: 70 General Instructions: 1. All questions are compulsory. 2. Section A contains 18 questions of 1mark each. 3. Section B contains 7 questions of 2marks each. 4. Section C contains 5 questions of 3marks each. 5. Section D contains 3 questions of 5marks each. 6. Section D contains 2 questions of 4marks each. SECTION-A 1. Two large metal sheets having surface charge density + and are kept parallel to each other at a small separation distance d. The electric field at any point in the region between the plates is a) / 0 b) /2 0 c) 2 / 0 d) /4 0 2. A point charge q is placed at one corner of a cube. The total flux through one of the the surface due to charge is a) q/3 0 b) q/6 0 c) q/8 0 d) q/24 0 3. N drops of mercury are charged simultaneously to 10 volt. When combined to form one large drop, the potential is found to be 40 volt, the value of N is...... a) 4 b) 6 c) 8 d) 10 4. Potential energy stored in electric dipole present in uniform electric field is a) x b) . c) . d) x 5. A cell of e.m.f E and internal resistance r is connected across a resistance r. The potential difference between the terminals of the cell must be a) E b) E/2 c) E/4 d) 3E/2 6. A wire carrying a steady current is first bent in form of a circular coil of one turn and then in form of a circular coil of two turns. Fine the ratio of magnetic fields at the centers of the two coils. a) 1:1 b) 1:4 c) 1:2 d) 4:1 7. In a series L, R, C, circuit which is connected to a.c. source. When resonance is obtained then net impedance Z will be a) Z=R b) Z= L -1/ C c) Z = L d) Z= 1/ C 8. Which part of the electromagnetic spectrum is used in night vision cameras? a) UV rays b) Radio wave c) Infrared Rays d) X-Rays 9. Displacement current is due to a) Change in magnetic flux b) Change in electric flux c) Motion of electrons d) Motion of holes 10. Electromagnetic waves can be polarised because em waves are ......... in nature. a) Mechanical b) Longitudinal c) Transverse d) Dual 11. Light waves from two coherent waves have amplitudes in the ratio 4:9. The ratio of maximum and minimum intensity is a) 25:1 b) 16:81 c) 3:2 d) 13:5 12. Photon of frequency (v) has a momentum associated with it. If (c) is the velocity of radiation, then the momentum is a) hv/c b) v/c c) hvc d) hv/c2 13. If the frequency of incident radiation falling on the cathode is increased then . Increases. a) Stopping Potential b) Photoelectric Current c) Work function d) Threshold frequncy 14. Value that can not be obtained from the graph between stopping potential and frequency of incident radiation is a) Work function b) Threashold frequency c) Planks constant d) Saturation current 15. When the conductivity of a semiconductor is due to the rupture of its covalent bonds only then the semiconductor is called a) Extrinsic b) Intrinsic c) Donor d) Acceptor Two statements are given Assertion (A) & Reason (B). Select the correct answer. a) Both A & R are true and R is the correct explanation of A. b) Both A & R are true But R is not the correct explanation of A. c) A is true but R is false d) Both A & R are false 16. Assertion: Voltmeter is connected in parallel with the circuit Reason: Resistance of voltmeter is very large. 17. Assertion: Kinetic energy of photoelectrons does not depend upon the intensity of incident radiation. Reason: Ejection of photoelectrons is not possible below threshold frequency. 18. ASSERTION: Total energy of an electron is negative. REASON: Kinetic Energy of an electron can not be negative. SECTION-B 19. Find the expression for internal resistance (r) of a cell having emf (E) connected to an external resistance (R) having terminal potential difference (V). 20. FInd the force acting on a current carrying wire placed in a uniform magnetic field. 21. How a galvanometer is converted into an ammeter? Or What is the necessary conditions for a charge to experience maximum force moving in external magnetic field. Find force also. 22. In Young double slit experiment the maximum intensity of light is k units. Find the intensity at a point where the path difference is /4. 23. An -particle and a Proton are accelerated through the same potential difference. Find the ratio of their de-Broglie wavelengths. 24. Find the ratio of longest & shortest wavelengths of Balmer series. OR Define Impact parameter, Find its value for the scattering angle, = 0o & 180o. 25. Discuss the role of a full wave rectifier. SECTION-C 26. State and prove the principle of Wheatstone bridge. 27. As shown in figure, a cell is connected across two points A and B of a uniform circular conductor. Prove that the magnetic field at its centre O will be zero. 28. A 200V variable frequency AC source is connected to a series combination of L=5H, C=80 F and R=40 at resonance. Find the following a) Angular frequency b) Current c) Power dissipated in the circuit. OR A transformer has 300 turns in the primary and 600turns in the secondary coil. The primary voltage is 250V and the load in the secondary is 50 .Find the following a) Voltage across secondary. b) Current in the secondary. c) Current in the primary. 29. A converging lens of refractive index 1.5 has a power of 10 D. When it is completely immersed in a liquid, it behaves as diverging lens of focal length 50cm. Find the refractive index of the liquid. 30. State Bohr s Quantisation condition. Using this condition show that radius of H atom is directly proportional to square of principal quantum number. OR Plot the variation showing variation between Binding Energy per nucleon & Mass number. What is the significance of this graph? SECTION-D 31. State Gauss theorem. Find the electric field due to an infinite uniformly charged wire of charged density . OR a) Find the capacitance of a parallel plate capacitor with dielectric slab of thickness (t) introduced between the plates. b) How will the capacitance of parallel plate capacitor change if area of the plates is halved and distance between plates is doubled. 32. Using Phasor diagram of series LCR circuit, find the expression of impedance. Also deduce the condition of resonance in the circuit. OR a) Define Faraday law and Lenz s law of electromagnetic induction. b) Find the expression of emf induced in an AC generator. 33. State Huygens Principle. Using Huygens Principle, deduce the laws of refraction of light. OR a) With the help of ray diagram, deduce the expression for magnifying power of an astronomical telescope at least distance of distinct vision. b) How reflecting type telescope is better than refracting type telescope? SECTION-E 34. When a beam of sunlight is incident on a glass prism, the emergent light splits into seven colours Violet, Indigo, Blue, Green, Yellow, Orange, Red (VIBGYOR). This phenomenon is called Dispersion of light and the the band of seven colours is called Spectrum. Dispersion is due to the refraction But refraction of different colours is due to different speed of different colours of light in a medium. (i) (ii) (iii) (iv) Name the Phenomenon involved in the formation of a band of seven colours is called Why Blue colour scatter more than Red State the condition for minimum deviation of light A prism is dipped into a liquid then how angle of deviation changes? 35. Two important processes are involved in the formation of p-n junction. Due to concentration gradient across p & n side of the junction , holes diffuse from p to n side and electrons diffuse from n to p side. This results in the setup of a layer of +ve ions on n side & a layer of ve ions on p side. These two layers of ions stops further diffusion of charges and drift the majority charges back to their original sides. (i) What is composition of Depletion layer in PN junction (ii) What is the effect of doping on width of depletion layer. (iii) Name the two Processes in the formation of depletion layer (iv) Why pure semiconductors behave like insulators at absolute zero temperature KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -3 CLASS : XII TIME: 3 hrs SUBJECT: PHYSICS M.M: 70 General Instructions:(1) There are 35 questions in all. All the questions are compulsory. (2) This question paper has five sections: Section A, Section B, Section C, Section D and section E. All the questions are compulsory. (3) Section A contains eighteen MCQ of 1 mark each, Section B contain seven questions of 2 marks each, Section C contains Five questions of three marks each , Section D contains three long questions of five marks each and Section E contains two case study based questions of 4 marks each. (4) There is no overall choice. However , an internal choice has been provided in section B,C,D and E. You have to attempt only one of the choices in such questions. (5) Use of calculator is not allowed. Section-A MARKS Q. No 1. Electric field lines contracts length wise, It shows 1 (A) Repulsion between same charges. (B) Attraction between opposite charges. (C) No relation between force and contraction. (D) Electric field lines do not move on straight path. 2. The work done in carrying a charge once round the circle of radius R 1 with charge Q at the centre of circle is (A) ZERO (B) KQ/R (C) KQ /R (D) KQ/R 3. Two wires A and B of same material, having radii in the ratio 1:2 and 1 carry currents in the ratio 4:1 . the ratio of the drift of electrons in A and B is- (A) 16:1 (B) 1:16 (C) 1:4 (D) 4:1 4. To convert a moving coil galvanometer into an ammeter of given 1 range, we must connect: (A) A suitable low resistance in series (B) A suitable low resistance in parallel (C) A suitable high resistance in parallel. (D) A suitable high resistance in series. 5. An electric current pass through a long straight copper wire. At a 1 distance 5 cm from the straight wire, the magnetic field is B. The magnetic at 20 cm from the straight wire would be (A) B/6 (B) B/4 (C) B/3 (D) B/2 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. A positive charge particle is moving with uniform velocity v enters a region of crossed electric and magnetic fields E and B and the positive particle remains undeflected from its path then (A) v = E + B (B) v= E/B (C) v= E.B (D) v= B/E If both the number of turns and core length of an inductor is doubled keeping other factors constant, then its self-inductance will be (A) Unaffected (B) Doubled (C) Halved (D) Quadrupled In electromagnetic waves the phase difference between electric field and magnetic field is (A) /2 (B) 0 (C) /4 (D) Which of the following quantity is increased in the step down transformer (A) Current (B) Voltage (C) Power (D) Frequency Air bubble in water behaves as (A) concave lens (B) convex lens (C) sometimes convex , sometime concave (D) plane glass slab For a given kinetic energy , which of the following has smallest de Broglie wavelength (A) Electron (B) Proton (C) Deutron (D) alpha particle On moving up in the energy states of a H-like atom , the energy difference between two consecutive energy states (A) decreases (B) increases (C) first increases then decreases (D) remains same Which of the following quantities is not conserved in a nuclear reaction (A) momentum (B) charge (C) mass (D) all of the above The phase difference between current and voltage in series LCR circuit at resonance is (A) (B) /2 (C) /4 (D) 0 In a region of constant potential (A) the electric field is uniform (B) electric field is zero (C) the electric field is decreasing (D) the electric field is increasing Two statements are given one labelled Assertion (A) and other labelled as Reason (R). Select the correct answer to these questions from the codes (A),(B),(C),(D) as given below. (A) Both A and R are true and R is the correct explanation of A (B) Both A and R are true and R is not the correct explanation of A 1 1 1 1 1 1 1 1 1 1 1 17. 18. (C) A is true but R is false (D) A is false and R is also false Assertion(A) :- conductivity of an n-type semiconductor is greater than that of a p-type semiconductor. Reason(R)- Electron have greater mobility than holes Two statements are given one labelled Assertion (A) and other 1 labelled as Reason (R). Select the correct answer to these questions from the codes (A),(B),(C),(D) as given below. (A) Both A and R are true and R is the correct explanation of A (B) Both A and R are true and R is not the correct explanation of A (C) A is true but R is false (D) A is false and R is also false Assertion(A)- A ray of light entering from glass to air suffers change in frequency. Reason( R)- velocity of light in glass is more than that in air Two statements are given one labelled Assertion (A) and other 1 labelled as Reason (R). Select the correct answer to these questions from the codes (A),(B),(C),(D) as given below. (A) Both A and R are true and R is the correct explanation of A (B) Both A and R are true and R is not the correct explanation of A (C) A is true but R is false (D) A is false and R is also false Assertion(A)- Photoelectric effect demonstrates the wave nature of light. Reason(R ) The number of photoelectrons is proportional to the frequency of light. Section-B 19. Name the electromagnetic radiation having the wavelength range 1 nm to 700 nm. Give its two important applications. 20. Write the expression for the force acting on a particle of mass m and charge q moving with velocity v in a magnetic field B. Under what condition the charge particle will move in a circular path. 21. What will be the angular momentum of the electron in Bohr s hydrogen atom whose energy is -3.4 eV ? OR Find the ionisation energy and ionisation potential of the ground state electron in hydrogen atom. 22. If half of the convex lens is painted black, then draw a ray diagram to show the image formation. How will this image formed by lens be different if the lens were not painted . 23. Draw the energy band diagram of an n-type and a p-type semiconductor at temperature T>0 K. Mark the donor and accepter energy levels with their energies. OR 2 2 2 2 2 24. 25. Distinguish between an intrinsic semiconductor and a n-type semiconductor. Why a n-type semiconductor is electrically neutral, although it has number of electrons much greater than number of holes. An object of size 3.0 cm is placed 14 cm in front of a concave lens of focal length of 21 cm. where is the image produced by the lens . what happens if the object is moved further away from the lens. Two fixed point charges +4q and +q units are separated by a distance a . Where should the third point charge be placed for it to be in equilibrium? Section C 26. A series LCR circuit is connected to an ac source. Using the phasor diagram , derive the expression for the impedence of the circuit . plot a graph to show the variation of the current with frequency of the source, explaining the nature of its variation. 27. Derive an expression for the torque acting on a current carrying loop in magnetic field. Name an instrument whose working is based on this concept. 28. How does mutual inductance of pair of coil changes when (1) Distance between the coils is increased (2) The number of turns in each coil is decreased. (3) A thin iron sheet is placed between two coils, other factors remaining the same OR (1) A conducting loop is held above a current carrying wire PQ as shown in fig. Depict the direction of current induced in the loop, when the current in the wire PQ is constantly increasing. 2 2 3 3 3 P Q (2) Lenz law obey law of conservation of mechanical energy. Justify the statement. 29. Draw a plot showing the variation of photoelectric current with 3 collector plate potential for two different frequencies and ( > ) of incident radiations having the same intensities. In which case will the stopping potential will be higher ? Why ? OR Sketch the graph , showing the variation of stopping potential with frequency of incident radiation for two photosensitive materials A and B having threshold frequencies > respectively. What information do you get from the graph. 30. When light of wavelength 400nm is incident on the cathode of a photocell ,the stopping potential recorded is 6 V. If the wavelength of the incident light is increased to 600nm , calculate the new stopping potential. Section D 31. (i)Using Gauss Theorem, derive an expression for electric field intensity at a point due to a infinitely long line of charge. (ii)Draw the variation of electric field intensity with the distance from the centre of a uniformly charged spherical shell. OR (i)A charge of 8mC is located at the origin . calculate the work done in taking a small charge of -2nC from a point P(0,0,3cm) to a point Q(0,4cm,0) via a point R(0,6cm,9cm) (ii) Four charges +q, -q , +q and -q are to be arranged respectively at the four corners of a square ABCD of a side a. (a) Find the work required to put together this arrangement. (b) A charge q is bought to the centre of the square, how much extra work is needed to do this ? 32. (i)Plot the graph showing variation of voltage vs the current drawn from the cell. Using this graph how we can find the emf of the cell and its internal resistance . (ii)Emf of a cell is 2 volt . A 10 ohm resistance is joined at its two ends then potential difference is measured 1.6 volt. Find the internal resistance of cell. OR (1) Define the term drift velocity. (2) On the basis of electron drift, derive an expression for resistivity of conductor in terms of number density of free electrons and relaxation time. (3) On what factors does resistivity of a conductor depends? 3 5 5 33. (i) Draw course of rays through a compound microscope. Deduce an 5 expression for its magnifying power. (ii) You are given two converging lens of focal length 1.25 cm and 5 cm to design a compound microscope. If it is desired to have a magnification of 30, find out separation between the objective and eye piece. OR (i)Deduce the conditions for constructive and destructive interference in terms of phase difference and path difference between two waves. (ii)Draw the variation of intensity of double slit interference pattern as a function of phase difference between waves. (iii)What happens if white light is used in young s double slit experiment. Section- E 34. Case study:The phenomena of total internal reflection takes place at the boundary between two transparent media when a light ray in a medium of higher refractive index of refraction approaches the other medium at an angle of incidence greater than the critical angle. Total Internal Reflection takes place in electromagnetic wave, sound wave as well as water wave. (i)Define critical angle between two transparent media. (ii) what are the conditions of Total Internal Reflection ? (iii) write a phenomena where Total Internal Reflection is Observed. OR critical angle for light passing from glass to air is minimum for which colour ? 35. Case study:When a diode is forward biased, it is found that beyond forward voltage , called knee voltage , the conductivity is very high . at this value of battery biasing for p-n junction, the potential barrier is overcome and the current increases in forward voltage . when the diode is reverse biased ,the reverse bias voltage produces a very small current about a few microamperes which almost remains constant with bias. This small current is called saturation current. 4 4 (i) draw the V-I graph in case of forward biasing and reverse biasing (ii) How does the thickness of depletion region changes in forward biasing. (iii) why does the reverse saturation current is very small , of the order of few microampere. OR Name a device which is used to convert alternating current into direct current. KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -4 CLASS : XII TIME: 3 hrs SUBJECT: PHYSICS M.M: 70 General Instructions: (1) There are 35 questions in all. All questions are compulsory (2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E. All the sections are compulsory. (3) Section A contains eighteen MCQ of 1 mark each, Section B contains seven questions of two marks each, Section C contains five questions of three marks each, section D contains three long questions of five marks each and Section E contains two case study-based questions of 4 marks each. (4) There is no overall choice. However, an internal choice may be provided. You have to attempt only one of the choices in such questions. (5). Use of calculators is not allowed. SECTION (A) 1. Two-point charges A and B, having charges +q and -q respectively, are placed at certain distance apart and force acting between them is F. if 25% charge of A is transferred to b, then force between the charges becomes: (a) F (c) 16F/3 (b) 9F/16 (d) 4F/3 2. The electric field due to a uniformly charged hollow sphere of radius R as a function of the distance from its centre is represented by 3. Four-point charges -Q, -q, 2q and 2Q are placed, one at each corner of the square. The relation between Q and q for which the potential energy at the centre of the square is zero is (a) Q=q/2 (c) Q=-q/2 (b) Q=-q (d) Q=q 4. In a Wheatstone bridge, all the four arms have equal resistance R. if resistance of the galvanometer arm is also R, then equivalent resistance of the combination is (a) R (c) R/2 (b) 2R (d) R/4 5. A current loop is placed in uniform magnetic field. The torque acting on it does not depend upon the (a) Shape of the loop (c) Value of current (b) Area of the loop (d) Magnetic field 6. In Bohr model, the atomic radius of the first orbit is R0. Then the radius of third orbit is (a) 3R0 (c) R0 /3 (b) 9 R0 (d) R0/9 7. Inductance of the coil is (a) Electrical Inertia (c) Source of emf (b) Force (d) Friction 8. Out of the following options which one can be used to produce a propagating electromagnetic wave? (a) A charge less particle (b) An accelerating charged particle (c) A stationary particle (d) A charge moving at constant velocity 9. Which of the following has the lowest frequency? (a) Infrared rays (c) UV rays (b) X-rays (d) -rays 10. Which of the following waves are used in telecommunication? (a) visible light (c) ultraviolet (b) microwaves (d) infrared 11. The condition for observing diffraction from a single slit is that the light wave front incident on the slit should be: (a) The size of slit should be equal (c) The size of slit should be comparable to wavelength lto wavelength (b) The size of slit should be greater (d) none of these than wavelength 12. The number of photoelectrons emitted from a photosensitive material is proportional to (a) Threshold frequency (c) Phase of the light (b) Intensity of light (d) Frequency of the light 13. If an electron and a photon having same wavelength, it implies that they have same (a) Speed (c) Energy (b) Momentum (d) All of the above 14. When light is incident at the metal surface, the emitted electrons: (a) are called photons (b) have energies that depend upon the intensity of light. (c) have equal energies. (d) have energies that depend upon the frequency of light. 15. In a good conductor, the energy gap between the valence and conduction bands is (a) 1eV (c) Infinite (b) 6eV (d) Zero Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true and R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is true Assertion: Voltmeter is connected in parallel with the circuit. Reason: Resistance of a voltmeter is very large. 17. Assertion: Electron has higher mobility than hole in a semiconductor. Reason: The mass of electron is less than the mass of the hole. 16. 18. Assertion: The focal length of the convex mirror will increase, if the mirror is placed in water. Reason: The focal length of a convex mirror of radius R is equal to, f = R/2. SECTION (B) 19. Establish a relation between electric current and drift velocity. 20. A circular coil of wire consisting of 100 turns, each of radius 8 cm carries a current of 0.40A. What is the magnitude of magnetic field B at the centre of the coil? OR Plot a graph between resistivity and temperature of a copper an nicrome 21. A galvanometer has resistance of 15 and the meter shows full scale deflection for a current of 4 mA. How will you convert the meter into an ammeter of range 0 to 6 A? 22. Draw the diagrams to show the behaviour of plane wave front as they pass through a (a) thin prism (b) reflect by concave mirror. 23. Calculate the kinetic energy of an electron having de- Broglie wavelength of 1 A0 24. The radius of innermost orbit of a hydrogen atom is 5.3 10-11m. What are the radii of n=2 and n=3 orbits? OR State & prove Bohr s Quantisation condition. 25. How does the resistivity of a semiconductor varies with temperature. Justify? SECTION (C) 26. Use Kirchhoff s rules to find the currents I1, I2, and I3, in the circuit diagram shown. 27. Show diagrammatically the behaviour of magnetic field lines in the presence of (i) paramagnetic and (ii) diamagnetic substances. How does one explain this distinguishing feature? 28. State Lenz s law. A metallic rod held horizontally along east-west direction, is allowed to fall under gravity. Will there be an induced emf at its ends? Justify your answer. 29. Use the mirror formula to show that a convex mirror always produces a virtual image independent of the location of the object? OR Why no interference pattern is observed when two coherent sources are (i) infinitely close (ii) far apart from each other. 30. Using photon picture of light, show how Einstein s photoelectric equation can be established. Write two features of photoelectric effect which cannot be explained by wave theory. OR (a) Define the terms (i) threshold frequency and (ii) stopping potential in photoelectric effect. (b) Plot a graph of photocurrent versus anode potential for a radiation of frequency and intensities I1 and I2 SECTION (D) 31. (a) Define Electric flux. Write its SI unit. (b) Using Gauss law, prove that electric field at any point due to a uniformly charged infinite plate sheet is independent of the distance from it. (c) How is the field directed if (i) the sheet is positively charged, (ii) negatively charged? OR Derive an expression for the capacitance of a parallel plate capacitor when a dielectric slab of dielectric constant K and thickness t = 2 but of same area as that of the plates is inserted between the capacitor plates. 32. Derive an expression for the self-inductance of a long air cored solenoid of length l, cross- sectional area A and having number of turns N. OR (a) What is impedance? (b) A series LCR circuit is connected to an ac source having voltage V=V0 sin t. Derive expression for the impedance, instantaneous current and its phase relationship to the applied voltage. Find the expression for the resonant frequency. 33. (a) A convex spherical surface of radius of curvature R, separates a rarer and denser medium. Hence Derive the relation connecting object distance u, image distance v, radius of curvature R and the refractive indices n1 and n2 of the two media, when object is placed in rarer medium. b) Explain how the focal length of a convex lens changes, with increase in the wavelength of incident light. OR Define the term wave front. Using Huygens wave theory, verify the laws of refraction. SECTION (E) 34. A P-N JUNCTION DIODE: p-n junction is a semiconductor diode. It is obtained by growing p-type semiconductor over an n- type semiconductor. A thin layer is developed at the p- n junction which is devoid of any charge carrier but has immobile ions. It is called depletion layer. At the junction a potential barrier appears, which does not allow the movement of majority charge carriers across the junction in the absence of any biasing of the junction. p-n junction offers low resistance when forward biased and high resistance when reverse biased. 1. What is the effect of reverse biasing of pn junction diode on depletion layer. 2.Which type of material has maximum forbidden energy band gap? 3. Name two processes involved in formation of pn junction diode. OR Define potential barrier. 35. Total internal reflection is the phenomenon of reflection of light into denser medium at the interface of denser medium with rarer medium. For this phenomenon to occur necessary condition is that light must move from denser to rarer and angle of incidence in denser medium must be greater than critical angle for the pair of media in contact. Critical angle depends on nature of medium and wavelength of light. We can show that =1/sinC (where C is the critical angle). (i) Find the Critical angle for glass air interface, if for glass is 3/2, (2) Explain the working of optical fiber. (3) What is reflecting prism KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -5 CLASS : XII SUBJECT: PHYSICS TIME: 3 hrs M.M: 70 General Instructions: 1. There are 35 questions in all. All questions are compulsory 2. This question paper has five sections: Section A, Section B, Section C, Section D and Section E. All the sections are compulsory. 3. Section A contains fifteen MCQ and three Assertion-Reason of 1 mark each, Section B contains seven questions of two marks each, Section C contains five questions of three marks each, section D contains three long questions of five marks each and Section E contains two case study based questions of 4 marks each. 4. There is no overall choice. However, an internal choice has been provided in section B, C, D and E. You have to attempt only one of the choices in such questions. 5. You may use the following values of physical constants where ever necessary. c = 3 X 108 m/s h = 6.63 X 10-34 Js e = 1.6 X 10-19 C = 4 X 10-7 TmA-1 = 8.854 X 10-12 C2N-1m-2 = 9 X 109 Nm2C-2 me = 9.1 X 10-31 kg mass of neutron = 1.675 X 10-27 kg mass of proton = 1.673 X 10-27 kg Avogadro s number = 6.023 X 1023 per gram mole Boltzmann constant = 1.38 X 10-23 JK-1 Section- A 1. The unit of electric potential is volt and it is equal to: (a) Joule/Coulomb (b) joule. Coulomb (c) Coulomb/joule (d)None of these 2. The magnetic field in a plane electromagnetic wave is given by: = 2 10 7 sin(0.5 103 + 2 23.9 109 ) The frequency of the wave is: (a) 0.5 103 (c) 23.9 109 (b) 2 0.5 103 (d) 2 23 109 3. Which of the material is most suitable for making connecting wires: (a) Nichrome (b) Tungsten (c)Copper (d)Manganese 4. The phase difference between electric field and magnetic field in an electromagnetic wave is: (a) (b) zero (c) 2 (d) 4 5. If the magnetic field is parallel to positive Y-axis and charged particle is moving along positive X-axis. The Lorentz force acts along negative Z -axis. The charge particle can be: (a) an electron (b) a proton (c) an alpha particle (d) both (b) and (c) 6. Which of the following is true for a conductor: (a) Inside a charged conductor, electrostatic field is zero (b) At the surface of a charged electrostatic potential is zero (c) The interior of a conductor can have excess charge in static situation (d) Electrostatic potential is constant throughout the volume of the solid conductor 7. The A proton and an -particle have the same de Broglie wavelength. What is same for both of them? (a) Mass (b) Energy (c) Frequency (d) Momentum 8. Plot of an angle 1 versus angle 2 is given for a triangular prism. The angle 1 & 2 respectively known as : (a) angle of incidence and angle of reflection (b) angle of incidence and angle of emergence (c) angle of incidence and angle of prism (d) angle of incidence and angle of deviation 9. A 44mH inductor is connected to 220V , 50Hz ac supply. The net power absorbed over a complete cycle will be: (a) 0W (b)4.4W (c)2400W (d)1100W 10. Threshold wavelength for a metal having work function W0 is . What is the threshold wavelength for a metal having work function 2 W0? (a) 4 (b) 2 (c) /2 11. When a forward bias is applied to a p-n junction, it (d) /4 (a) raises the potential barrier. (b) reduces the majority carrier current to zero. (c) lowers the potential barrier. (d) None of the above. 12. Two point charges +2C and +6C repel each other with a force of 12 newton. If a charge of 4C is given to each of these charges the force now is (a)Zero (b)4 N (attractive) (c)12 N (attractive) (d)8 N (repulsive) 13. In photoelectric effect, the K.E of photoelectrons emitted is proportional to (a) Intensity of incident beam (b) frequency of incident beam (c) Velocity of incident beam (d) work function of photocathode. 14. If , , are the speed of gamma rays, X-rays and microwaves respectively in vacuum then: (a) > > (b) < < (c) > < (d) = = 15. For a closed surface the Gauss s law is___________________________________ (a) independent of shape of the surface (b) Independent of size of the surface (c) Both a and b. (d) None of these. For question numbers 16, 17, and 18, two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true but R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is also false 16. Assertion(A): As work function of a material increases by some mechanism, it requires greater energy to eject the electrons from its surface. Reason(R): A plot of stopping potential (V) versus frequency (v) for different materials, has greater slope for metals with greater work functions 17. Assertion(A): Nuclear force is same between neutron-proton, proton-proton & neutron-neutron. Reason(R):Nuclear force is charge independent. 18. Assertion(A): In a metallic wire if we increase the temperature of wire the resistance of the wire also increases. Reason(R): On increasing the temperature thermal velocity of electrons increases and relaxation time period decreases in this way number of collision increases. Section- B 19. Draw a plot showing the variation of binding energy per nucleon with mass number Write two important conclusions that you can draw from this plot. 20. Draw the circuit diagram of full wave rectifier adnd also draw its input and output wave forms. OR How is forward biasing different from reverse biasing in a p-n junction diode? 21. Use Kirchhoff s rule to obtain balance condition in Wheatstone bridge. 22. Three identical specimen of magnetic material Nickle, antimony and aluminium are kept in uniform magnetic field. Draw the modification of filed lines in each case. Which magnetic property distinguish this behaviour of magnetic field lines? 23. de Broglie wavelength associated with an electron accelerated through a potential difference V is . What will be de Broglie wavelength when the accelerating potential is increased to 4 V? Or Work function of Sodium is 2.3 . Does Sodium show Photoelectric emission for orange light ( = 6800 ) 24. A convex lens of focal length f dipped in the trasparenbt liquid of refractive index l. If refractive index of liquid is more than that of glass. Show that the focal length of lens increases in liquid. Or 1 1 1 1 2 Establish the relation = + for two co-axial thin lens in contact with each other. 25. Using bio savart law, find the expression for magnetic field at the centre of a circular loop . Section- C 26. What do you mean by power of a lens? Give its unit also. A converging lens has a focal length of 20 cm when immersed in water. What is its nature and power? (Absolute refractive index of glass = 1.5 and absolute refractive index of water = 1.33) Or A point object is placed in front of a convex refracting surface. Derive the expression for u , v and R for this surface. 27. Define drift velocity of electron. Using drift velocity deduce Ohm s Law. 28. The Biot-Savart law for magnetic field has certain similarities as well as differences with coulomb s law for electrostatic field. Write any three such points for similarities and differences. 29. A circular coil of radius 10 cm 500 turns and resistance 2 ohm is places with the plane perpendicular to a magnetic field 3 10 5 . It is rotated about vertical diameter through 180 in 0.25 s. Estimate the magnitude of average emf induced in the coil. 30. Find the ratio of longest & shortest wavelengths of Balmer series. Or Using Bohr s postulates of atomic model, derive the expression of radius of nth orbit. Hence find the Bohr s radius. Section- D 31. a) Draw a labelled diagram showing the formation of image at least distance of distinct vision by a compound microscope. Hence obtain expression for its magnifying power. b) A small object is placed at a distance of 3.0 cm from a magnifier of focal length 4.0 cm. Find: i. ii. The position of image formed The linear magnification produced. Or a) With the help of a ray diagram explain the working of reflecting type telescope. Mention two advantages of reflecting telescope over a refracting telescope. b) A small telescope has an objective lens of focal length 1.4 m and an eye piece of focal length 5.0 cm. calculate magnifying power of telescope when telescope is in normal adjustment. 32. a) Derive an expression for intensity of electric field due to an electric dipole at any point on its equatorial line. b) Two point charges = 3 and = 3 are located 20 cm apart in vacuum. Calculate electric field at the mid-point of the line joining two charges. Or a) Using Gauss s law, derive an expression for electric field near a infinite long straight conductor. b) Two large metal plate are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite sign and of magnitude 17 10 22 C/m2 . Calculate the electric field between the plates. 33. a) Write the principles of working of an a.c generator. Derive and expression for induced emf in it. b) The armature in a.c generator has 200 turns and area 0.1 m2 Calculate the angular speed of coil , so that the peak value of induced emf is 250 V. The coil is rotated in a magnetic field of 0.25 Tesla. Or For an ideal conductor connected across an ac voltage source,state with reason,which of the following quantities will be zero? a) Instantaneous Power, (b) Average power over full cycle of the ac voltage source Section- E 34. Mirage:A mirage is a naturally occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. Under certain conditions, such as over a stretch of pavement or desert air heated by intense sunshine, the air rapidly cools with elevation and therefore increases in density and refractive power. Sunlight reflected downward from the upper portion of an object for example, the top of a camel in the desert will be directed through the cool air in the normal way. Although the light would not be seen ordinarily because of the angle, it curves upward after it enters the rarefied hot air near the ground, thus being refracted to the observer s eye as though it originated below the heated surface. A direct image of the camel is seen also because some of the reflected rays enter the eye in a straight line without being refracted. The double image seems to be that of the camel and its upside-down reflection in water. When the sky is the object of the mirage, the land is mistaken for a lake or sheet of water. 1. Write two application of TIR. 2. Write essential condition for TIR. 3. Two lens of power +5D and -3D are placed in contact. Finbd the focal length of the combination. 4. Draw the graph angle of incidence and angle pof deviation for a prism. OR Define critical angle and write its relation b/w refractive index. 35. p-n junction is a semiconductor diode. It is obtained by bringing p-type semiconductor in close contact with n- type semiconductor. A thin layer is developed at the p- n junction which is devoid of any charge carrier but has immobile ions. It is called depletion layer. At the junction a potential barrier appears, which does not allow the movement of majority charge carriers across the junction in the absence of any biasing of the junction. p-n junction offers low resistance when forward biased and high resistance when reverse biased. 1. What is the electric field at the middle of depletion layer of reverse biased p- n junction. [1] 2. Define potential barrier. OR Name the minority charge carrier in extrinsic semiconductor [1] 3. Draw the enrgy band diagram for P type and N type semiconductor. [2] KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -6 CLASS : XII SUBJECT: PHYSICS TIME: 3 hrs M.M: 70 Time Allowed: 3 hours. General Instructions: (1) There are 35 questions in all. All questions are compulsory. (2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E. All the sections are compulsory. (3) Section A contains eighteen MCQ of 1 mark each, Section B contains seven questions of two marks each, Section C contains five questions of three marks each, section D contains three long questions of five marks each and Section E contains two case study based questions of 4 marks each. (4) There is no overall choice. However, an internal choice has been provided in section B, C, D and E. You have to attempt only one of the choices in such questions. (5). Use of calculators is not allowed. SECTION-A 1. Why Silicon is more widely used for semiconductor devices? (A) It can be used at much higher temperatures than germanium. (B) It is cheaper than germanium. (C) It has higher conductivity than germanium. (D) None of the above. 2. Photoelectric current depends on (a) Intensity of light (b) frequency of light (c) both a and b (d) work function of metal. 3. Which Quantity is vector Quantity among the following (a) Electric flux (b) Electric charge (c) Electric field (d) Electric potential 4. Electric field line contracts length wise ,It shows (a) repulsion between same charges (b) Attraction between apposite charges (c) No relation between force & contraction. (d) Electric field lines does not moves on straight path. 5. A dipole is placed parallel to electric field. If W is the work done in rotating the dipole from 0 to 60 , then work done in rotating it from 0 to 180 is (a) 2 W (b) 3 W (c) 4 W (d)6W 6. Work done to bring a unit positive charge un-accelerated from infinity to a point inside electric field is called : (A) Electric field (B) Electric potential (C) Capacitance (D) Electric flux 7. Kirchhoff s II law for the electric network is based on: (a) Law of conservation of charge (b) Law of conservation of energy (c) Law of conservation of angular momentum (d) Law of conservation of mass 8. Current sensitivity of a galvanometer can be increased by decreasing (a) Magnetic field B (b) number of turns N (c) torsional constant K (d) Area A 9. In Faraday s experiment on electromagnetic induction, more deflection will be shown by galvanometer, when (a) Magnet is in uniform motion towards the coil (b) Magnet is in uniform motion away from the coil (c) Magnet is in accelerated motion towards the coil (d) Magnet is at rest near the coil 10. EM waves can be produced by a charge: (a) An accelerated charged particles (b) A charged particles moving with constant speed (c) at rest. (d) either at rest or moving with constant velocity. 11. In EM spectrum minimum wavelength is of: (a) gamma rays (b) radio waves (c) visible rays (d) microwave. 12. Which of the following transport by EM waves: (a)charge & momentum (b) frequency & wavelength (c) energy & momentum (d) wavelength & energy 13. Ratio of intensities of two waves are given by 4:1. Then ratio of the amplitudes of the two waves is (a) 2:1 (b) 1:2 (c) 4:1 (d) 1:4 14. The maximum kinetic energy of photoelectrons emitted from a surface when photons of energy 6 eV fall on it is 4 eV. The stopping potential, in volt is (a) 2 (b) 4 (c) 6 (d) 10 15. A particle of mass M at rest decays in to two particles of masses m1 and m2 having non zero velocities. The ratio of the de-Broglie wavelength of the particles 1/ 2 is (a) m1/ m2 (b) m2/ m1 (c) 1 (d) (m2)2 / (m1)2 Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b Both A and R are true and R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is also false 16. Assertion (A): In balanced condition, if the galvanometer and the voltage source is interchanged, the balanced condition remains same. Reason (R): The balanced condition of Wheatstone bridge does not depend on the value of the resistances. 17. Assertion (A): A photon has no rest mass, yet it carries definite momentum. Reason (R): Momentum of photon is due to its energy and hence its equivalent mass 18. Assertion (A): According to Rutherford, atomic model, the path of an electron is parabolic. Reason (R): Rutherford could not explain the stability of the atom. SECTION-B 19. Two electric bulbs P and Q have their resistances in the ratio of 1: 2. They are connected in series across a battery. Find the ratio of the power dissipation in these bulbs. 20. Write two points of differences between para, dia and ferromagnetic materials, giving one example for each. 21. Write expression for Lorentz force in vector form. If a charged particle enters in a uniform magnetic field at right angles then find the nature of path and hence find the radius 22. Define the terms depletion layer and Potential barrier. 23. The ground state energy of hydrogen atom is -13.6 eV. If an electron makes a transition from an energy level-1.51 eV to -3.4 eV, calculate the wavelength of the spectral line emitted and the series of hydrogen spectrum to which it belongs. OR The short wavelength limit for the Lyman series of the hydrogen spectrum is 913.4 A 0. Calculate the short wavelength limit for the Balmer series of the hydrogen spectrum. 24. A proton and an alpha particle are accelerated with the same accelerating potential. Find the ratio between their de-Broglie wavelengths. 25. A biconvex lens made of a transparent material of refractive index 1.25 is immersed in water of refractive index 1.33. Will the lens behave as a converging or a diverging lens? Justify your answer. SECTION-C 26. Draw a plot of potential energy of a pair of nucleons as a function (i) Write two important conclusions that can be drawn from the graph. (ii)What is the significance of negative potential energy in the graph drawn? 27.a). State Huygen s principle for construction of wave. (b). Verify the law of reflection using the Huygen s principle. 28. (a) What is the principle of a moving coil galvanometer . (b) Give two reasons to explain why a galvanometer cannot as such be used to measure the value of the current in a given circuit. (c) Define the terms: (i) voltage sensitivity and (ii) current sensitivity of a galvanometer. 29. Use Kirchhoff's rules to obtain conditions for the balance condition in a Wheatstone bridge. 30. (a) A capacitor is connected with a voltage source V= V0 sin wt. Find the expression for electric current through the circuit. Draw the phasor diagram showing current and voltage. OR An inductor is connected with a voltage source V= V0 sin wt. Find the expression for inductive reactance. Plot inductive reactance with frequency. SECTION-D 31. (a) Use Gauss' theorem to find the electric field due to a uniformly charged infinitely large plane thin sheet with surface charge density . (b) An infinitely large thin plane sheet has a uniform surface charge density + . Obtain the expression for the amount of work done in bringing a point charge q from infinity to a point, distant r, in front of the charged plane sheet. OR A capacitor of capacitance C, is charged to a potential V, while another capacitor of capacitance C, is charged to a potential difference V, The capacitors are now disconnected from their respective charging batteries and connected in parallel to each other. (i) Find the total energy stored in the two capacitors before they are connected. (ii) Find the total energy stored in the parallel combination of the two capacitors. (iii) Explain the reason for the difference of energy in parallel combination in comparison to the total energy before they are connected. 32. i) Draw a labelled ray diagram for the formation of image by a compound microscope in normal adjustment. (ii) Define magnifying power of a compound microscope in normal adjustment and derive an expression for it. (iii) Compound microscope uses an objective lens of focal length 4 cm and eyepiece lens of focal length 10 cm. An object is placed at 6 cm from the objective lens. Calculate the magnifying power of the compound microscope if final image is formed at infinity. Also calculate the tube length of the microscope. OR (a) Draw a labelled ray diagram to obtain the real image formed by an astronomical telescope in normal adjustment position. Define its magnifying power. (b) You are given three lenses of power 0.5 D, 4D and 10 D to design a telescope. (i)Which lenses should be used as objective and eyepiece? Justify your answer. (ii) Why is the aperture of the objective preferred to be large? 33. (a) Draw a labelled diagram of a transformer. Obtain the ratio of secondary to primary voltage in terms of number of turns and currents in the two coils. (b) A power transmission line feeds input power at 2200 V to a step-down transformer with its primary windings having 3000 turns. Find the number of turns in the secondary to get the power output at 220 V. OR (a)A circular coil of radius 8.0 cm and 20 turns is rotated about its vertical diameter with an angular speed of 50 rad s-1 in a uniform horizontal magnetic field of magnitude 3.0 10-2 T. Obtain the maximum and average emf induced in the coil. If the coil forms a closed loop of resistance 10 , calculate the maximum value of current in the coil. Calculate the average power loss due to Joule heating. (b)Current in a circuit falls from 5.0 A to 0. 0 A in 0.1 s. If an average emf of 200 V induced, give an estimate of the self-inductance of the circuit. SECTION-E 34. Read the below text and answer any four of questions that follow: The total internal reflection of light is used in diamond polishing to create a gleaming brilliance. It is adjusted by polishing the diamond with specific cuts so that the majority of light rays approaching the surface are incident with an angle of incidence greater than the critical angle. As a result, they are subjected to multiple reflections and eventually emerge from the top of the diamond. This gives the diamond a brilliant gleam. 1. What is the cause of brilliance of Diamond? 2. Name one application of use of Total Internal reflection in the field of medical science. 3. Give two advantages of reflecting type telescope over refracting type telescope. OR The speed of light in diamond is 125,000 km s-1. What is the refractive index of diamond? (speed of light in air = 3 x 108 m s-1). 35. Read the below text and answer any four of questions that follow: Band theory of solid: Consider that the Si or Ge crystal contains N atoms Electrons of each atom will have discrete energies in different orbits. The electron energy will be same if all the atoms are isolated, ie, separated from each other by a large distance. However, in a crystal, the atoms are close to each other (2 A to 3 A) and therefore the electrons interact with each other and also with the neighbouring atomic cores. The overlap (or interaction) will be more felt by the electrons in the outermost orbit while the inner orbit or core electron energies may remain unaffected. Therefore, for understanding electron energies in Si or Ge crystal, we need to consider the changes in the energies of the electrons in the outermost orbit only. For Si, the outermost orbit is the third orbit (n=3), while for Ge it is the fourth orbit (n = 4). Each Si and Ge has four valence electrons, but Ge at a given temperature has more free electrons and a higher conductivity compared to Si. So, silicon is more widely used for semiconductor devices, since it can be used at much higher temperature than germanium. 1. When the energy of electrons of atoms of a substance will be same? 2. What do you mean by doping? Name the types of dopants in semiconductors OR Name the additional energy level formed in extrinsic semiconductors. 3. Draw the energy band diagram for Si and Ge. KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -7 CLASS : XII TIME: 3 hrs SUBJECT: PHYSICS M.M: 70 General Instructions: There are 35 questions in all. (1) All questions are compulsory (2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E. All the sections are compulsory. (3) Section A contains eighteen MCQ of 1 mark each, Section B contains seven questions of two marks each, Section C contains five questions of three marks each, section D contains three long questions of five marks each and Section E contains two case study based questions of 4 marks each. (4) There is no overall choice. However, an internal choice has been provided in section B, C, D and E. You have to attempt only one of the choices in such questions. (5) Use of calculators is not allowed. 1. 2. 3. 4. 5. What is the minimum charge on a particle? (a) 1 Coulomb (b) 1.6 x 10-19 Coulomb (c) 3.2 x 10-19 Coulomb (d) 6.6 x 10-19 Coulomb For a hollow spherical shell, potential, V changes with respect to distance, r from the centre. Which graph from the following represents this? 1 1 In parallel combination of n cells, we obtain 1 (a) more voltage (b) more current (c) less voltage (d) less current In a permanent magnet at room temperature 1 (a) magnetic moment of each molecule is zero. (b) The individual molecules have non-zero magnetic moment which is all perfectly aligned. (c) Domains are partially aligned. (d) Domains are all perfectly aligned. The net magnetic flux through any closed surface, kept in a magnetic field is 1 (a) zero 6. 7. 8. 9. 10. 11. 12. 13. (b) 0/4 (c) 4 / 0 (d) 4 0/ If an electron is moving with velocity produces a magnetic field B , when it will exert maximum force (a) the direction of field B will be same as the direction of velocity (b) the direction of field B will be opposite to the direction of velocity (c) the direction of field B will be perpendicular to the direction of velocity (d) the direction of field B does not depend upon the direction of velocity The nature of parallel and anti-parallel currents are (a) parallel currents repel and anti-parallel currents attract. (b) parallel currents attract and anti-parallel currents repel. (c) both currents attract. (d) both currents repel. Which of the following laws was modified by Maxwell by introducing the displacement current? (a) Gauss s law (b) Ampere s law (c) Biot-Savart s law (d) None of these A transformer is used to light 100 W and 110 V lamps from a 220 V mains. If the main current is 0.5 A. Then the efficiency of the transformer is: (a) 11% (b) 50% (c) 80% (d) 90% Two coherent monochromatic light beams of intensities I and 4I superimpose. The maximum and minimum possible intensities in the resulting beam are: (a) 5I and I (b) 5I and 3I (c) 3I and I (d) 9I and I Heavy stable nuclei have more neutrons than protons. This is because of the fact that (a) neutrons are heavier than protons. (b) Electrostatic force between protons is repulsive. (c) Neutrons decay into protons through beta decay. (d) Nuclear forces between neutrons are weaker than that between protons. The strength of photoelectric current depends upon : (a) angle of incident radiation. (b) frequency of incident radiation. (c) intensity of incident radiation. (d) distance between anode and cathode. The work function for a metal surface is 4.14 eV. The threshold wavelength for this metal surface is: a) 4125 b) 2062.5 c) 3000 d) 6000 1 1 1 1 1 1 1 14. 15. 16. 17. 18. 19. 20. The no. of turns in the primary coil of a transformer is 200 and the no. of turns in 1 the secondary is 10. If 240 V a.c. is applied to primary, the output from the secondary (a) 6 V (b) 12 V (c) 24 V (d) 48 V Which of the following statements is false for a perfect conductor? 1 (a) The surface of the conductor is an equipotential surface. (b) The electric field just outside the surface of a conductor is perpendicular to the surface. (c) The charge carried by a conductor is always uniformly distributed over the surface of the conductor. (d) None of these. Two statements are given-one labelled Assertion (A) and the other labelled 1 Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true and R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is also false A) de- Broglie equation is significant for microscopic particles. B) de- Broglie wavelength is inversely proportional to the mass of a particle when velocity is kept constant. Two statements are given-one labelled Assertion (A) and the other labelled 1 Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true and R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is also false A) The energy gap between the valance band and conduction band is greater in germanium than in silicon. B) Heat energy produces fewer minority carriers in germanium than in silicon. Two statements are given-one labelled Assertion (A) and the other labelled 1 Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true and R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is also false A) Wavefront emitted by a point source of light in an isotropic medium is spherical. B) Isotropic medium has same refractive index in all directions. SECTION B How are infrared waves produced? What is the range of their wavelength? Write two factors by which voltage sensitivity of a galvanometer can be increased. 2 2 21. Draw a plot of potential energy of a pair of nucleons as a function of their separations. Mark the regions where the nuclear force is (i) attractive and (ii) repulsive. Write any two characteristic features of nuclear forces. Or Two nuclei have mass number of 8 & 27. Find the ratio of their nuclear radius and their nuclear densities. 2 22. A converging lens of refractive index 1.5 is kept in a liquid medium having same refractive index. What would be the focal length of the lens in this medium? What is doping? Write the name of the impurities used to fabricate p type & n type semiconductor. OR Draw the energy band diagram of conductor , insulator and semiconductor. In a single slit diffraction experiment, the width of the slit is reduced to half its original width. How would this affect the size and intensity of the central maximum? Two point charges 4Q, Q are separated by 1 m in air. At what point on the line joining the charges is the electric field intensity zero? SECTION C What is the magnitude of magnetic force per unit length on a wire carrying a current of 8 A, making an angle of 30 with the direction of a uniform magnetic field of 0.15 T? 2 23. 24. 25. 26. 27. 28. 29. 2 2 2 3 Derive the expression for force per unit length between two long straight parallel 3 current carrying conductors. Hence, define one ampere. a) Draw a labelled diagram of AC generator and state its working principle. 3 b) How is magnetic flux linked with the armature coil changed in a generator? Or A voltage V = V0 sin wt is applied to a series L-C-R Derive the expression for the average power dissipated over a cycle. Under what condition is a) No power dissipated even though the current flows through the circuit. b) Maximum power dissipated in the circuit? a) The figure shows a plot of three curves a, b, c showing the variation of 3 photocurrent vs collector plate potential for three different intensities I1, I2 and I3 having frequencies v1, v2 and v3 respectively incident on a photosensitive surface. Point out the two curves for which the incident radiations have same frequency but different intensities. b) The maximum kinetic energy of a photoelectron is 3eV. What is its stopping potential? OR a) Define intensity of radiation in photon picture of light. Write its SI unit. b) Plot a graph showing the variation of photo current vs collector potential for three different intensities I1>I2>I3, two of which (I1 and I2) have the same frequency and the third has frequency > 1. 30. Find the ratio of energies of photons produced due to transition of an electron of hydrogen atom from its 3 a) second permitted energy level to the first permitted level and b) The highest permitted energy level to the first permitted level. 31. 32. SECTION - D a) Using Gauss law, obtain the expression for the electric field due to 5 uniformly charged spherical shell of radius R at a point i) outside the shell ii) inside the shell . b) Given a uniform electric field E =5 x 103 i N/C, find the flux of this held through a square of 10 cm on a side whose plane is parallel to the YZ-plane. What would be the flux through the same square if the plane makes an angle of 30 with the X-axis? OR a) Define the dipole moment of an electric dipole. Write its SI units. How does the electric potential due to a dipole vary on the dipole axis as a function of r distance of the point from the mid-point of the dipole at large distances? b) Deduce the expression for the potential energy of a system of two point charges q1 and q2 brought from infinity to the points with positions and r2 respectively, in presence of external electric field E. a) In an experiment on meter bridge, student obtains the balance point at the 5 point J such that AJ=40cm, as shown in figure. The values of R and X are both doubled and then interchanged. Find the new position of the balance point. If the galvanometer and battery are also interchanged how will the position of balance point be affected? b) Answer the following (i) Why are the connections between the resistors in a meter bridge made of thick copper strips? (ii)Why is it generally preferred to obtain the balance point in the middle of the meter bridge wire? (iii)Which material is used for the meter bridge wire and why? OR a) Derive an expression for drift velocity of free electrons in a conductor in terms of relaxation time. b) The plot of the variation of potential difference across a combination of three identical cells in series, versus current is shown below. What is the emf and internal resistance of each cell? The emf of a cell is always greater than its terminal voltage. Why? Give reason. 33. a) Use Huygens geometrical construction to show how a plane wave front at 5 t = 0 propagates and produces a wave front at a later time. b) Verify, using Huygens Principle, Snell s law of refraction of a plane wave propagating from a denser to a rarer medium. c) When monochromatic light is incident on a surface separation two media, the reflected and refracted light both have the same frequency. Explain why? OR a) In Young s double slit experiment, describe briefly how bright and dark fringes are obtained on the screen kept in front of a double slit. Also write down the conditions for constructive and destructive interference. b) The ratio of the intensities at minima to the maxima in the Young s double slit experiment is 9:25. Find the ratio of the widths of the two slits. SECTION E 34. CASE STUDY: 4 As we know that, when light ray travels from one medium to another changes its direction of path due to the change in optical density of the medium. When light ray travels from optically denser medium to the optically rarer medium then some of the light get reflected back in the same medium and remaining light get refracted in the second medium and such a phenomenon of light is called as internal reflector light. We know that, when a ray of light travels from denser medium to rarer medium then it get bended away from the normal. If we increase the angle of incidence slowly then angle of refraction also gets increased and at one stage the angle of refraction is 90 for some angle of incidence. And further if we increase the angle of incidence then there will be no refraction of light and the ray will be totally internally get reflected. Such phenomenon of reflection of light is called as total internal reflection of light. And the angle of incidence in denser medium for which the angle of refraction in rarer medium is 90 , that angle of incidence is called as critical angle. So we define total internal reflection as, if the angle of incidence exceeds the critical angle then the total light get internally reflected. Mirage is the best real life example of total internal reflection of light. The highly brilliance of diamonds is only due to the total internal reflection of light through them which is get total internally reflected many times and causes brilliance of diamonds. Prisms are also made by using total internal reflection of light. We all know that, optics is the vast branch of physics which has vast application in our daily life such as optical fibre. Optical fibre is used for long distance transmission of audio and video signal also. And they are mainly constructed on the basis of total internal reflection of light to reduce the decrease in amplitude of the sending signal. Questions: Q 1) What is the value of angle of refraction for critical angle? Q 2)Write down the conditions for Total Internal Reflection. Q 3) Why, In case of total internal reflection, for angle of incidence greater than critical angle the refraction of light is not possible? 4) Write down the relation between critical angle and refractive index. 0r 5) How total internal reflection of light would be possible in case of optical fibres? 35. CASE STUDY: 4 Materials are classified on the basis of their conductivity as metals, semiconductors and insulators. Metals are having low resistivity and high conductivity. While semiconductors are having resistivity and conductivity in between metals and insulators. And finally insulators are those which are having high resistivity or very low conductivity. Semiconductors may exist as elemental semiconductors and also compound semiconductors. Si and Ge is elemental semiconductor and CdS, GaAs, CdSe, etc. are the compound semiconductors. Each electron in an atom has different energy level and such different energy levels continuing forms the band of energy called as energy bands. That energy band which has energy levels of Valence electrons is called as Valence band. And the energy band which is present above the Valence band is called as conduction band. On the basis of energy bands materials are also defined as metals, semiconductors and insulators. In case of metals, conduction band and Valence band overlaps with each other due to which electrons are easily available for conduction. In case of insulators, there is some energy gap between conduction band and Valence band due to which no free electrons are easily available for conduction. And in semiconductors, there is a small energy gap between conduction band and Valence band and if we give some external energy then electron from Valence band goes to conduction band due to which conduction will be possible. These semiconductors are classified as intrinsic semiconductors and extrinsic semiconductors also. Intrinsic semiconductors are those semiconductors which exist in pure form. And intrinsic semiconductors has number of free electron is equal to number of holes. The semiconductors doped with some impurity in order to increase its conductivity are called as extrinsic semiconductors. Questions: Q 1) Name the impurity atom to obtain p type & n type semicondor. 1 Or What is the condition for intrinsic semiconductor? Q 2) Name the material which have energy band gap Eg > 3 eV Q 3) Differentiate between p type & n type semi conductors. 1 2 KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -8 CLASS : XII SUBJECT: PHYSICS TIME: 3 hrs M.M: 70 General Instructions: (1) There are 35 questions in all. All questions are compulsory (2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E. All the sections are compulsory. (3) Section A contains eighteen MCQ of 1 mark each, Section B contains seven questions of two marks each, Section C contains five questions of three marks each, section D contains three long questions of five marks each and Section E contains two case study based questions of 4 marks each. (4) There is no overall choice. However, an internal choice has been provided in section B, C, D and E. You have to attempt only one of the choices in such questions. You may use the following values of physical constants wherever necessary. c = 3 x 108 m/s h = 6.63 x 10-34Js e = 1.6 x 10-19 C o = 4 x 10-7 T m A-1 0 = 8.854 x 10-12 C2 N-1 m-2 1 = 9 x 109 N m2 C-2 4 me = 9.1 x 10-31 kg mass of neutron = 1.675 x 10-27 kg mass of proton = 1.673 x 10-27 kg Avogadro s number = 6.023 x 1023 per gram mole Boltzmann constant = 1.38 x 10-23 JK-1 Sr.No. 1. Marks Section A All questions are compulsory. In case of internal choices, attempt any one of them. Five balls numbered 1 to 5 balls suspended using separate threads. Pair (1,2), (2,4) 1 and (4,1) show electrostatic attraction, while pair (2,3) and (4,5) show repulsion. Therefore ball 1 must be (a) Positively charged (b) Negatively charged (c) Neutral (d)Made of metal 2. Two small, identical spheres having +Q and Q charge are kept at a certain 1 distance. F force acts between the two. If in the middle of two spheres, another similar sphere having +Q charge is kept, then it experience a force in magnitude and direction as (a) Zero having no direction (b) 8F towards +Q charge (c) 8F towards Q charge (d) 4F towards +Q charge 3. Equal charges Q are placed at the vertices A and B of an equilateral triangle ABC of side a. The magnitude of electric field at the point A i Q 2Q 4 0 a 2 1 Q 3Q 4 0 a 2 4. 4 0 a 2 0 a (a) (b) (c) (d) The amount of work done in increasing the voltage across the plates of a capacitor From 5 V to 10 V is W. The work done in increasing it from 10 V to 15 V will be a) 0.6 W (b) W (c) 1.25 W (d) 1.67 W 5. For a cell, the terminal potential difference is 2.2 V when the circuit is open and 1 2 2 1 reduces to 1.8 V, when the cell is connected across a resistance, R = 5 . The internal resistance of the cell is (a) 6. 10 9 9 (b) 10 11 (c) 9 5 (d) 9 Two solenoids having current I and 2I and the number of turns N and 4N, then 1 the ratio of the magnetic field will be (a 1: 8 7. (b) 2 : 1 9 10 11. (d) 4 : 1 A current carrying solenoid is approaching a conducting loop as shown in the figure. The direction of induced current as observed by an observer on the other side of the loop will be (a)Anticlockwise (b)Clockwise (c)East (d)West 8. (c) 1 : 4 1 v Observer An electromagnetic radiation has an energy 14.4 KeV. To which region of electromagnetic spectrum does it belong (a)Infra red region (b)Visible region (c)X-rays region (d) -ray region Which of the following EMW has highest wavelength? (a) X-ray (b) ultraviolet rays (c) infrared rays (d) microwaves Choose the wrong statement? (a)Electromagnetic waves are transverse (b) Electromagnetic waves travel with the speed of light in free space (c) Electromagnetic waves are produced by accelerating charges (d) Electromagnetic waves travel with the same speed in all media A ray of light is incident at the glass water interface at an angle i, it emerges finally 1 1 1 1 parallel to the surface of water, then the value of g would be (a)(4/3) sin i (b)1/ sin i Water (c)4/ 3 Glass (d)1 12 w=4/3 r r i The de-Broglie wavelength of a electron accelerated with 100 volt potential, its wavelength will be 1 (a)0.123 13 (b) 1.23 (c)12.3 (d) 0.0123 The work function of a substance is 4.0 eV. The longest wavelength of light that 1 can cause photoelectron emission from this substance is approximately (a)540 nm 14 (b) 400 nm (c)310 nm (d)220 nm Photo-energy 6 eV are incident on a surface of work function 2.1 eV. What is the 1 Kinectic energy (a) 5V 15 16 17 (b) 1.9 V (c) 3.9 V (d) 8.1 V A p-type semiconductor is: (a) negatively charged (b) positively charged (c) uncharged (d) None of these 1 For question numbers 16, 17,and 18, two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true but R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is also false Assertion (A): In the process of nuclear fission, the amount of nuclear energy 1 generated by the fission of an atom of uranium is so tremendous that it produces 10 million times the energy produced by the combustion of an atom of carbon from coal. Reason(R): The nucleus of a heavy atom such as uranium, when bombarded with low-energy neutrons, splits apart into lighter nuclei. The mass difference between the original nucleus and the product nuclei gets converted to tremendous energy. Assertion (A): Ohm s law is universally applicable for all conducting elements 1 Reason(R): All conducting elements show straight line graphic variation on (IV)plot. 18 Assertion (A): Kinetic energy of photo electrons emitted by a photosensitive surface depends upon the intensity of incident photon. 1 Reason(R): The ejection of electrons from metallic surface is possible with frequency of incident photon below the threshold frequency. Section B All questions are compulsory. In case of internal choices, attempt anyone. 2 19 Define current sensitivity and voltage sensitivity of a galvanometer. Increasing the current sensitivity may not necessarily increase the voltage sensitivity of a galvanometer. Justify. 20 What are diamagnetic and ferromagnetic substance. Write its two properties. 1,1 OR What is the function of radial field in the moving coil galvanometer? 21 An electron beam is moving between two parallel plates having electric field 2 1.125 10-6 V/m. A magnetic field 3 10 10T is also applied, so that beam of electrons does not deflect. What is the velocity of the electron? 22 Two Sources of Intensity I and 4I are used in an interference experiment. Find the intensity at points where the waves from two sources superimpose with a phase difference (i) zero (ii) . 2 OR Find the ratio of fringe width of interference pattern of two coherent sources having wavelength 400 nm and 700 nm. 23 Show the variation of photocurrent with collector plate potential for different frequencies but same intensity of incident radiation. 2 24 Explain the second postulates of Bohr s model of hydrogen atom. 2 25 Draw the circuit diagram used to determine the VI characteristics of forward and reverse biasing. 2 26. 27 Section -C All questions are compulsory. In case of internal choices, attempt any one. (i) write down the unit and dimension of coefficient of self induction. (ii) A small piece of metal wire is dragged across the gap between the pole piece of a magnet in 0.5 sec. The magnetic field is 8 X 10-4 wb. Estimate the emf induced in the wire. Apply bio savart law to derive an expression for the magnetic field at the centre of a current carrying circular loop. OR The field B at the centre of a circular coil of radius r is times that due to a long straight wire at a distance r from it, for equal currents here shows three cases; in all cases the circular part has radius r and straight ones are infinitely long. For same current find the magnetic field B at the centre P in cases 1, 2, 3. 1. 2. i i r O 28 29 3 3. r O 3 i r O 90o Two batteries A and B each of emf 2 volt are connected in series to external 3 resistance R = 1 . Internal resistance of A is 1.9 and that of B is 0.9 , what is the potential difference between the terminals of battery A. 3 A convex lens has a focal length 0.2 m in air and is made of glass ( =1.50) is immersed in water ( =1.33). Find the change in focal length of the lens. OR Draw a ray diagram of showing the image formation by a compound microscope. 30. 31 32 33 2 4 The binding energy per nucleon of deuteron (1 H ) and helium nucleus (2 He ) is 1.1 MeV and 7 MeV respectively. If two deuteron nuclei react to form a single helium nucleus, find the Q energy released during the reaction. Section D All questions are compulsory. In case of internal choices, attempt any one. (a) A series LCR circuit is connected to an a.c. source of variable frequency. Draw a suitable phasor diagram to deduce the expressions for the amplitude of the current and phase angle. (b) Obtain the condition at resonance. Draw a plot showing the variation of current with the frequency of a.c. source for two resistances R1 and R2 (R1 > R2). OR (a)Draw a labelled diagram of a.c. generator and state its working principle. b)How is magnetic flux linked with the armature coil changed in a generator ? (c) Derive the expression for maximum value of the induced emf in generator and state the rule that gives the direction of the induced emf. (i)For a ray of light traveling from a denser medium of refractive index n 1 to a rarer medium of refractive index n2, prove that c=sin-1(n2/n1).Where c is the critical angle of incidence for the media (ii) Explain with the help of a diagram, how the above principle is used for transmission of video signals using optical fibres. OR i)Find the expression for the conditions of constructive and destructive in Young s double slit experiment. ii)What is the effect on the fringe width if the whole apparatus (YDSE) is completely immersed in a liquid of refractive index ? i)Find the expression for the capacitance of a parallel plate capacitor of area A and plate separation d ii)(a) a dielectric slab of thickness t, and (b) a metallic slab of thickness t, where t < d are introduced one by one between the plates of the capacitor. In which case would the capacitance be more and why? OR i)Three charges, each equal to +2C are placed at the corners of an equilateral triangle. If the force between any two charges be F, then what will be the net force on either Charge? ii) Derive an expression for the torque on an electric dipole in a uniform electric field. Section E Questions 34 and 35 are Case Study based questions and are compulsory. Attempt any 4 sub parts from each question. Each question carries 1 mark. 34. Power of a lensPower (P) of a lens is given as the reciprocal of focal length (P=1/f)where f should be in meter and P is in Diopter . for convex power is positive and concave power is ve. When two or more lenses are kept in contact then power of the combined lens is given as P= P1 + P2+P3 . 3 5 5 5 35. 1. A student use the lens of focal length -40cm. What will be the power of the lens. 1 2. What is the effective power of two lenses of power +1.5D and +1.0D when they are placed in contact with each other. 3. Define one diopter. 1 4. What is the power of a lens and its write down its unit. 1 1 TYPES OF SEMICONDUCTOR Semiconductors may exist as elemental semiconductors and also compound semiconductors. Si and Ge are elemental semiconductor and CdS, GaAs, CdSe, anthracene, polypyrrole etc. are the compound semiconductors. Each electron in an atom has different energy level and such different energy levels continuing forms the band of energy called as energy bands. Those energy band which has energy levels of Valence electrons is called as Valence band. And the energy band which is present above the Valence band is called as conduction band. On the basis of energy bands materials are also defined as metals, semiconductors and insulators. In case of metals, conduction band and Valence band overlaps with each other due to which electrons are easily available for conduction. In case of insulators, there is some energy gap between conduction band and Valence band due to which no free electrons are easily available for conduction. And in semiconductors, there is a small energy gap between conduction band and Valence band and if we give some external energy then electron from Valence band goes to conduction band due to which conduction will be possible. These semiconductors are classified as intrinsic semiconductors and extrinsic semiconductors also. Intrinsic semiconductors are those semiconductors which exist in pure form. And intrinsic semiconductors has number of free electron is equal to number of holes. The semiconductors doped with some impurity in order to increase its conductivity are called as extrinsic semiconductors. Two types of dopants are used they are trivalent impurity and pentavalent impurity also. The extrinsic semiconductors doped with pentavalent impurity like Arsenic, Antimony, Phosphorus etc are called as n type semiconductors. When trivalent impurity is like Indium, Boron, Aluminium etc are added to extrinsic semiconductors then p type semiconductors will be formed. In p type semiconductors holes are majority charge carriers and electrons are the minority charge carriers. 1) What is electrically charged on P type semiconductor. 1 2) How can we convert an intrinsic semiconductor into N type semiconductor 1 2 3)Discuss the effect of temperature on semiconductor OR Draw the energy band for metal and semiconductor. KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -9 CLASS : XII SUBJECT: PHYSICS TIME: 3 hrs M.M: 70 General Instructions: (1) There are 35 questions in all. All questions are compulsory (2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E. All the sections are compulsory. (3) Section A contains eighteen MCQ of 1 mark each, Section B contains seven questions of two marks each, Section C contains five questions of three marks each, section D contains three long questions of five marks each and Section E contains two case study based questions of 4 marks each. (4) There is no overall choice. However, an internal choice has been provided in section B, C, D and E. You have to attempt only one of the choices in such questions. You may use the following values of physical constants wherever necessary. c = 3 x 108 m/s h = 6.63 x 10-34Js e = 1.6 x 10-19 C o = 4 x 10-7 T m A-1 0 = 8.854 x 10-12 C2 N-1 m-2 1 = 9 x 109 N m2 C-2 4 me = 9.1 x 10-31 kg mass of neutron = 1.675 x 10-27 kg mass of proton = 1.673 x 10-27 kg Avogadro s number = 6.023 x 1023 per gram mole Boltzmann constant = 1.38 x 10-23 JK-1 SECTION A MULTIPLE CHOICE QUESTIONS: 1. The oscillating electric and magnetic field vectors in an electromagnetic wave are (i) perpendicular to each other and opposite in phase. (ii) parallel to each other and opposite in phase. (iii) perpendicular to each other and in the same phase. (iv) parallel to each other and in the same phase. 2. For constructive interference to take place between two monochromatic light waves of wavelength , the path difference should be (i) (2n-1) /4 (ii) (2n-1) /2 (iii) n (iv) (2n+1) /2 3. An iron cored coil is connected in series with an electric bulb with an AC source as shown in figure. When iron piece is taken out of the coil, the brightness of the bulb will (i) decrease (iii) remain unaffected (ii) increase (iv) fluctuate 4. In a Young s double slit experiment, the path difference at a certain point on the screen between two interfering waves is 1/8th of the wavelength. The ratio of intensity at this point to that at the Centre of a bright fringe is close to (i) 0.80 (ii) 0.74 (iii) 0.94 (iv) 0.84 5. If the reading of the voltmeter V1 is 40 V, then the reading of voltmeter V2 is (i) 30 V (ii) 58 V (iii) 29 V (iv) 15 V 6. A proton moves through a uniform magnetic field, the force acting on it will (i) change both its kinetic energy and momentum (ii) change only its KE (iii) neither change its energy nor its momentum (iv) change only its momentum. 7. The work function for a metal surface is 4.14 eV. The threshold wavelength for this metal surface is: (i) 4125 (ii) 2062.5 (iii) 3000 (iv) 6000 8. Eddy currents are produced in a material when it is (i) its length (ii) placed in time varying magnetic field (iii) placed in an electric field (iv) placed in uniform magnetic field 9. A Step-up transformer operates at 230 V line and current supplied to a load is 2A. The ratio of primary and secondary windings is 1:25. The primary current is (i) 12.5A (ii) 50A (iii) 8.8 A (iv) 25A 10. The mean value of ac emf 200sin100 t is (i) 200 2V (ii) 200/ 2V (iii) 400V (iv) None of these 11. What will be the speed of light in the core, whose critical angle is 30 degree? (a) 3.0 x 108 m/s (b) 2.5 x 108 m/s (c) 1.5 x 108 m/s (d) 0.5 x 108 m/s Q 12. A positively charged particle is released from rest in a uniform electric field. The electric potential energy of the charge (1) remains a constant because the electric field is uniform. (2) increases because the charge moves along the electric field. (3) decreases because the charge moves along the electric field. (4) decreases because the charge moves opposite to the electric field. Q 13. The electric potential V at any point O (x, y, z all in metres) in space is given by V = 4x volt. The electric field at the point (1 m, 0, 2 m) in volt/metre is (1) 8 along negative x-axis (2) 8 along positive x-axis (3) 16 along negative x-axis (4) 16 along positive z-axis Q.14 A wire has resistance 16 . It is bent in the form of an equilateral triangle. The effective resistance between the two points on any median of the triangle is (1)16 (2)8 (3)4 (4)32 Q.15 . The current in a metallic conductor is plotted against voltage at two different temperatures T1 and T2. Choose the correct answer. (1)T1 > T2 (2)T1 < T2 (3)T1 = T2 (4)None ASSERTION AND REASONING For question numbers 11 to 16, two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true but R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is also false 16. Assertion(A): Electric filed lines not form closed loops. Reason(R): Electric filed lines are always normal to the surface of a conductor. 17. Assertion (A): In an interference pattern observed in Young's double slit experiment, if the separation (d) between coherent sources as well as the distance(D) of the screen from the coherent sources both are reduced to 1/3rd, then new fringe width remains the same. Reason (R): Fringe width is proportional to (d/D). 18. Assertion (A): The torque acting on square and circular current carrying coils having equal areas, placed in uniform magnetic field, will be same. Reason (R): Torque acting on a current carrying coil placed in uniform magnetic field does not depend on the shape of the coil, if the areas of the coils are same. SECTION B 19. A charge q is moved from a point A above a dipole of dipole moment p to a point B below the dipole in equatorial plane without acceleration. Find the work done in this process. 20. The electric potential V as a function of distance X is shown in the figure. Draw the graph of the magnitude of electric field intensity E as a function of X. 21. How does resistivity vary with temperature? 22. Write the expression for fringe width in young s double slit experiment. 23. Predict the direction of induced current in the situation described by the following Fig 24. Draw the graph between stopping potential and intensity. 25. Write the expression for the de Broglie wavelength associated with an electron accelerated through a potential V. SECTION C 26. You are given the following three lenses. Which two lenses will you use as an eyepiece and as an objective to construct an astronomical telescope? Give reason. OR Establish a relation between drift velocity vd of an electron in a conductor of cross-section A , carrying current i and concentration n of free electrons per unit volume of conductor. Hence obtain the relation between current density and drift velocity. 27. The graph shows the variation of photocurrent for a photosensitive metal (a) What does X and A represent on horizontal axis? (b) Draw this graph for three different values of frequencies of incident radiation 1, 2 and 3 ( 3> 2> 1) for the same intensity. (c) Draw this graph for three different values of intensities of incident radiation I 1, I2 and I3 (I3> I2>I1) having the same frequency. 28. Derive an expression for the self inductance of two long coaxial solenoids of same length wound one over the other. Or State faraday s law of electromagnetic induction and explain three methods of producing induced emf. 29. An equiconvex lens forms two times enlarged real image when an object is kept 16 cm from it. The lens is cut into two identical plano-convex lenses. If the object is again kept 16 cm in front of one of these lenses, then find the nature and position of the image formed. 30. With the help of a ray diagram, show the formation of image of a point object by refraction of light at a spherical surface separating two media of refractive indices n 1 and n2 (n2>n1) respectively. Using this diagram, derive the relation n2/v -n1/u= n2-n1/R Hence obtain an expression for lens maker s formula in the case of thin convex lens. SECTION D 31. (a) Using Gauss law, derive expression for electric field due to a spherical shell of uniform charge distribution and radius R at a point lying at a distance x from the centre of shell, such that (i) 0 < x < R, and (ii) x > R. (b) (i)Draw a plot showing the variation of photoelectric current with collector potential for different frequencies but same intensity of same radiation. (ii) What change do you observe if intensity of radiation incident on photosensitive surface is changed but the frequency remains the same. Or (a)In Young s double slit experiment, deduce the conditions for obtaining constructive and destructive interference fringes. Hence, deduce the expression for the fringe width. (b) Why cannot two independent monochromatic sources produce sustained interference pattern? (c) Two coherent light sources, whose intensities have the ratio of 100:1, produce interference fringes. Calculate the ratio of intensity of maxima and minima in the fringe system. 32 (a) Define wavefront. Verify using Huygens principle, Snell s law of refraction of a plane wave propagating from a denser to a rarer medium. (b) Do the speed and frequency change when light passes from a rarer into a denser medium? Or A device X is connected across an ac source of voltage V = V0 sin t. The current through X is given as I = I0 sin ( t + /2). (a) Identify the device X and write the expression for its reactance. (b) Draw graphs showing variation of voltage and current with time over one cycle of ac, for X. (c) How does the reactance of the device X vary with frequency of the ac? Show this variation graphically. (d) Draw the phasor diagram for the device X. 33. (a) Draw the graph showing intensity distribution of fringes with phase angle due to diffraction through a single slit. What is the width of the central maximum in comparison to that of a secondary maximum? (b) A ray PQ is incident normally on the face AB of a triangular prism of refracting angle 600 as shown in figure. The prism is made of a transparent material of refractive index 2/ 3. Trace the path of the ray as it passes through the prism. Calculate the angle of emergence and the angle of deviation. Or (a)Write two points of difference between an interference Pattern and a diffraction pattern. (b) (i) A ray of light incident on face AB of an equilateral glass prism, shows minimum deviation of 30 . Calculate the speed of light through the prism. (ii) Find the angle of incidence at face AB so that the emergent ray grazes along the face AC. CASE STUDY: 34. Read the following paragraph and answer the questions: A number of optical devices and instruments have been designed and developed such as periscope, binoculars, microscopes and telescopes utilizing the reflecting and refracting properties of mirrors, lenses and prisms. Most of them are in common use. Our knowledge about the formation of images by the mirrors and lenses is the basic requirement for understanding the working of these devices. (i) Why the image formed at infinity is often considered most suitable for viewing. Explain (ii) In modern microscopes multicomponent lenses are used for both the objective and the eyepiece. Why? (iii) Write two points of difference between a compound microscope and an astronomical telescope OR (iii) Write two distinct advantages of a reflecting type telescope over a refracting type telescope. Q.35 A transformer is a static electrical machine which transfers AC electrical power from one circuit to other at a constant frequency, but voltage can be altered according to the requirement. Number of turns in the primary and secondary coil decides a transformer to be step up or step down. 1. On which principle transformer works. 2. What is the function of Laminated iron core in transformer. 3. What is the condition of step up and step down transformer. 4. Explain the role of Soft iron core used in transformer. KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -10 CLASS : XII SUBJECT: PHYSICS TIME: 3 hrs M.M: 70 General Instructions: (1) There are 35 questions in all. All questions are compulsory (2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E. All the sections are compulsory. (3) Section A contains eighteen MCQ of 1 mark each, Section B contains seven questions of two marks each, Section C contains five questions of three marks each, section D contains three long questions of five marks each and Section E contains two case study based questions of 4 marks each. (4) There is no overall choice. However, an internal choice has been provided in section B, C, D and E. You have to attempt only one of the choices in such questions. 5. Use of calculators is not allowed. SECTION A Q.No. 1 Two point charges A and B, having charges +Q and -Q respectively, are placed at certain distance apart and force acting between them is F. If 25% charge of A is transferred to B, then force between the charges becomes : 2 3 (a) F (b) 9F / 16 (c) 16F / 9 (d) 4F/3 In which of the following cases the electric field at the centre is not zero ? Electric field intensity at a point in between two parallel sheets with like charges of same surface charge densities ( ) is (a) /2 0 4 (b) 3 / 0 (c) 2 / 0 Marks 1 1 1 (d) Zero An electric dipole of dipole moment 4 x 10-5 Cm, kept in a uniform electric field of 10-3 NC-1, experiences a torque of 2 x10-8 Nm. The angle which the dipole makes with electric field is : (a) 300 (b) 600 (c) 450 (d) 900 1 5 6 7 An ammeter of resistance 0.2 ohm and range 10 mA is to be used to read potential difference upto 1V. It can be converted into a voltmeter of desired range by connecting (a) 96 ohm in series (b) 92 ohm in parallel (c) 99.8 ohm in series (d) 90 ohm in parallel The relative permeability of iron is 6000. Its magnetic susceptibility is : (a) 5999 (b) 6001 (c) 6000 x 10-7 (d) 6000 x 107 The current I in a coil varies with time as shown in figure below. 1 1 1 The variation of induced emf with time would be : 8 9 10 11 12 If the angle of prism is 600 and angle of minimum deviation is 400, then angle of refraction will be : (a) 30 (b) 40 (c) 200 (d) 300 The electromagnetic waves are produced when a charge is (a) Moving with a constant velocity (b) Moving in a circular orbit (c) Falling in an electric field (d) Both (b) and (c) An em wave is propagating in a medium with a velocity v = v i. The instantaneous oscillating electric field of this wave is along + y axis. Then the direction of oscillating magnetic field of the em wave will be along : (a) y axis (b) z axis (c) - z axis (d) - x axis Which rays are not the portion of em waves ? (a) X rays (b) Microwaves (c) Alpha rays (d) Radio-waves Which of the following statement is incorrect about of photon ? (a) Energy of photon is h . 1 1 1 1 1 (b) Photon energy is dependent of intensity of radiation. (c) Photons are electrically neutral. (d) Number of photons may not be conserved in a collision. 13 14 15 16 The stopping potential as a work function of frequency of incident radiation is plotted for two different photo electric surfaces A and B. The graphs shows the work function of A is (a) greater than that of B (b) smaller than that of B (c) same as that of B (d) no comparison can be done from given graph The work function of a metal is 4.2 eV, its threshold wavelength is : (a) 4000 (b) 3500 (c) 2945 (d) 2500 When a forward bias is applied to a p-n junction, it (a) increases the potential barrier (b) reduces the majority carrier current to zero (c) decreases the potential barrier (d) all of the above Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true and R is NOT the correct explanation of A 1 1 1 1 c) A is true but R is false d) A is false and R is also false ASSERTION: No work is done in taking a positive charge from one point to other inside a positively charged sphere while outside the sphere work is done in taking the charge toward the sphere. REASON: Inside the sphere electric potential is same at each potential, but outside it is different for different points. 17 Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true and R is NOT the correct explanation of A c)A is true but R is false d)A is false and R is also false 1 ASSERTION: The light of a single frequency is incident on a metal surface, the energies of emitted photoelectrons are different. REASON: The energy of electrons emitted from inside the metal surface is lost in collision with the other atoms in the metal. 18 Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true and R is NOT the correct explanation of A 1 c) A is true but R is false d) A is false and R is also false ASSERTION: Total energy of an electron is negative. REASON: Kinetic Energy of an electron cannot be negative. SECTION B Derive an expression for the resistivity of a good conductor, in terms of 19 the relaxation time of electrons. Or The resistance of a given piece of wire is 10 . What will happen to its resistance & resistivity when its length is doubled? Write the expression for the force acting on a particle of mass m and 20 charge q moving with velocity in a magnetic field. Under what conditions will it move in (i) a circular path and (ii) a helical path ? 2 2 21 Using Ampere s circuital law, obtain the expression for the magnetic field at the centre of a circular coil carrying current. 2 22 Calculate the binding energy per nucleon of Fe5626 Given mFe = 55.934939 u, mn = 1.008665 u and mp = 1.007825 u. Two identical coherent waves each of intensity I0 are producing interference pattern. What are the values of resultant Intensity at a point of (i) constructive interference and (ii) destructive interference pattern ? 2 23 2 OR Use Huygen s principle to verify to laws of refraction. 24 (i) Draw a plot showing the variation of photoelectric current with 2 collector potential for different frequencies but with same intensity of incident radiations. (ii) What change will you observe if the intensity of incident radiation is changed but the frequency remains the same ? 25 Draw energy band diagrams of n-type of p-type semiconductors at temperature T > 0 K. Mark the donor and acceptor energy levels with their energies 2 SECTION C State Kirchoff s laws of current distribution in an electrical network. 26 3 Using these rules determine the current between B and D in the circuit diagram as shown in the figure below. OR Two cells of emf 1 and 2 having interrnal resistance r1 and r2 respectively are connected in parallel. Deduce the expressions for the equivalent emf and equivalent resistance of the combination. 27 A bar magnet of magnetic moment 1.5 J T 1 lies aligned with the direction of a uniform magnetic field of 0.22 T. 3 (a) What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment: (i) normal to the field direction, (ii) opposite to the field direction? (b) What is the torque on the magnet in cases (i) and (ii) ? OR A short bar magnet of magnetic moment m = 0.32 JT 1 is placed in a uniform magnetic field of 0.15 T. If the bar is free to rotate in the plane of the field, which orientation would correspond to its (a) stable, and (b) unstable equilibrium? What is the potential energy of the magnet in each case? 28 A voltage V = V0 sin t is applied to a series LCR circuit. Derive the expression for the average power dissipated over a cycle. Under what condition is (i) (ii) no power dissipated even though the current flows through the circuit, maximum power dissipated in the circuit? 3 29 30 31 Obtain Lens makers formula using the expression n2/v n1/u=(n2 n1)/R, 3 here the ray of light propagating from a rarer medium of refractive index (n1) to a denser medium of refractive index (n2) is incident on the convex side of spherical refracting surface of radius of curvature R. (i) State Bohr s quantization condition for defining stationary orbits. 3 How does de-Broglie hypothesis explain the stationary orbits ? (ii) Find the relations between the three wavelengths 1, 2 and 3 from the energy level diagram shown below. SECTION D (a) Use Gauss law to derive the expression for the electric field due to a straight uniformly charged infinite line of density Cm-1. (b) Draw a graph to show the variation of E with the perpendicular distance r from the line of charge. (c) Two large thin plates are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite signs and of magnitude 17 x 10 22 Cm-2. What is E : (i) in the outer region of first plate (ii) between the plates ? OR (a) Two charges 5 10 8 C and 3 10 8 C are located 16 cm apart. At what point(s) on the line joining the two charges is the electric potential zero? Take the potential at infinity to be zero. (b) A parallel plate capacitor with air between the plates has a capacitance of 8 pF (1pF = 10 12 F). What will be the capacitance 5 if the distance between the plates is reduced by half, and the space between them is filled with a substance of dielectric constant 6? 32 A X is connected to an ac source V = V0 sin t. The current I = I0 sin ( t - 2 ). The variation of voltage, current and power in one cycle is shown in the following graph : (i) Identify the device X . (ii) Which of the curves A, B and C represent the voltage, current and power in the circuit ? Justify your answer. (iii) How does its impedance vary with frequency of the ac source ? Show graphically. (iv) Obtain the expression for the current in the circuit and its phase relation with ac voltage. (v) At very high frequency a.c., capacitor behaves as a conductor. Why ? OR The Primary coil of an ideal step up transformer has 100 turns and transformation ratio is also 100. The input voltage and power are respectively 220 V and 1100 W. Calculate ( i) number of turns in secondary (ii) current in primary (iii) current in secondary (iv) power in secondary (v) Out of the arrangements given below for windings of primary and secondary colis in a transformer, which arrangement do you think will have higher efficiency and why ? 5 33 (a) In Young s double slit experiment, deduce the condition for (a) constructive , and (b) destructive interference at a point on the screen. Draw a graph showing the variation of intensity in the interference pattern x on the screen. (b) A beam of light consisting of two wavelengths 650 nm and 520 nm is used to obtain interference fringes in a YDSE. The distance between two slits is 2mm and distance between the plane of the slits and the screen is 1.2 m. What is the least distance from the central maximum where the bright fringes due to both the wavelengths coincide ? 5 OR (i) Draw the ray diagram showing the refraction of light through the glass prism and hence obtain the relation between the refractive index of the prism, angle of prism and angle of minimum deviation. (ii) A converging lens has a focal length of 20 cm in air. It is made of a material of refractive index 1.6. If it is immersed in a liquid of refractive index 1.3, find its new focal length. SECTION E 34 Case Study : Read the following paragraph and answer the questions An astronomical telescope is an optical instrument which is used for observing distinct images of heavenly bodies like stars, planets etc. It consists of two lenses. In normal adjustment of telescope, the final image is formed at infinity.To increase magnifying power of an astronomical in normal adjustment, focal length of objective lens should be large and focal length of eye lens should be small. (i) (ii) What is the condition for the focal lengths of objective lens and eye piece, for magnifying power of astronomical telescope ? Why the objective lens has a larger focal length and a larger aperture than the eyepiece ? (iii) An astronomical telescope of magnifying power of 7 consists of the two thin lenses 40 cm apart, in normal 4 adjustment. Find the focal length of the lenses OR An astronomical telescope of magnifying power of 10. In normal adjustment, distance between objective and eye piece is 22 cm. Find the focal length of objective lens. 35 Case Study : Read the following paragraph and answer the questions A pure semiconductor germanium or silicon, free of every impurity is called intrinsic semiconductor. At room temperature, a pure semiconductor has very small number of current carriers (electrons and holes). Hence its conductivity is low. When the impurity atoms of valancy five or three are doped in a pure semiconductor, we get respectively n-type or p-type extrinsic semiconductor. In case of doped semiconductor ne nh = ni2 Where ne and nh are the number density of electron and hole charge carriers in a pure semiconductor. The conductivity of extrinsic semiconductor is much higher than that of intrinsic semiconductor. (i) What is n-type semiconductor? (ii)Do pure semiconductors obey Ohm s law? (iii)Why do semiconductors behave as conductors at room temperature? OR Why does a semiconductor behaves as an insulator at very low temperature? 4 KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -1 SUBJECT: PHYSICS M.M: 70 CLASS : XII TIME: 3 hrs General Instruction : (i) All questions are compulsory. (ii) There are 35 questions in total. Questions 1 to 18(SECTION A) are multiple choice/AR type questions and carry one mark each. (iii) Questions 19 to 25(SECTION B) carry two marks each, questions 26 to 30(SECTION C) carry three marks each, and questions 31 to 33(SECTION D) carry five marks each and question 34,35(SECTION E) are case study based (iv) There is no overall choice. However, an internal choice has been provided in two question of two marks, two questions of three marks and all three question of five marks each weightage. You have to attempt only one of the choices in such questions. (v) Use of calculators is not permitted. However, you may use log tables if necessary. (vi) you may use the following values of physical constants wherever necessary. c = 3 108 m/s 1 4 o = 9 109 N m2 C 1 h = 6.63 10 34 Js e = 1.6 10 19 C me = 9.1 10 31 kg Mass of Neutrons = 1.675 10 27 kg 0 = 4 10 7 T mA 1 Mass of proton = 1.673 10 27 kg ***************************** Assertion Reason Type questions Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect. (SECTION A) 1. A hemisphere is uniformly charged positively. The electric field at a point on a diameter away from the centre is directed (a) (b) (c) (d) perpendicular to the diameter parallel to the diameter at an angle tilted towards the diameter at an angle tilted away from the diameter. 2. Consider a uniform electric field in the z direction. The potential is a constant (a) for any x for a given z. (b) for any y for a given z. (c) on the x-y plane in the given z (d) all the above 3. Out of following options which one can be used to produce a propagating electro-magnetic wave. a) Stationary Charge b) Chargeless Particle c) d) Accelerating Charge Charge moving with constant velocity. 4. Which of the following characteristics of electrons determines the current in a conductor? (a) Drift velocity alone. (b) Thermal velocity alone. (c) Both drift velocity and thermal velocity. (d) Neither drift nor thermal velocity. 5. The electric potential on the axis of an electric dipole at a distance r from it s centre is V .Then the potential at a point at the same distance on its equatorial line will be a) 2 V (b) V 6. which material has negative susceptibility (a) paramagnetic (b) Diamagnetic ( C ) V/2 ( d ) Zero (c) Ferromagnetic (d) nones 7. The Self inductance L of a solenoid of length l and area of cross- section A, with a fixed number of turns N increases as (a) l and A increase. (b) l decreases and A increases. (c) l increases and A decreases. (d) both l and A decrease 8. The amount of work done in bringing a unit positive charge from infinity to a point in electric field is represented by (a) Coulomb force (b) electric field (c) electric potential (d) electric potential diffrence 9. The velocity of em radiation in a medium of permittivity and perameability is given by (a) (b) (c) 1 (d) 10. There are three wavelengths 107m, 10-10m, & 10-7m. Find their respective names (a) Radio waves, X- rays, visible rays (b) X- rays, visible rays, Radio waves (c) X- rays, Gamma rays, visible rays (d) none of the above 11. Velocity of light in a liquid is 1.5 x 108m/s and in air it is 3 x 108m/s. If ray of light passes from liquid into the air than the critical angle of liquid is (a) 15 (b) 30 . (c) 45 . (d) none of the above 12. Assertion: The slope of the plot of Einstein s photoelectric equation is equal to Planck s constant. Reason: The intercept made by the plot of Einstein s photoelectric equation on the frequency axis is equal to threshold frequency of the metal. 13. Assertion : Voltmeter is connected in parallel with the circuit. Reason: Resistance of a voltmeter is very large. 14. Stopping potential for a metal surface in case of photo electric emission depends on? (a) The threshold frequency for the metal surface. (b) The incident light (c) The frequency of incident light (d) None of these. 15. A proton, a neutron, an electron and an -particle have same energy. Then their de Broglie wavelengths compare as (a) p = n > e > (b) < p = n > e (c) e < p = n > (d) e = p = n = 16. Kinetic energy of emitted electrons depends upon : (a) frequency (b) intensity (c) nature of atmosphere surrounding the electrons (d) none of these 17. Assertion : Between any two given energy levels, the number of absorption transitions is always less than the number of emission transitions. Reason : Absorption transitions start from the lowest energy level only and may end at any higher energy level. But emission transitions may start from any higher energy level and end at any energy level below it. 18. hole is (a) an anti-particle of electron. (b) a vacancy created when an electron leaves a covalent bond. (c) absence of free electrons. (d) an artificially created particle. (SECTION B) 19. A convex lens of focal length 25 cm is placed coaxially in contact with a concave lens of focal length 20 cm. Determine the power of the combination. Will the system be converging or diverging in nature? OR A converging lens of focal length f1 is placed co-axially in contact with diverging lens of focal length f2 (f2 > f1). Determine the power and nature of combination. 20. Define drift velocity. Write its relationship with relaxation time in terms of electric field E applied to the conductor. How does the drift velocity of electron affected when applied potential difference is doubled and length of conductor is halved. OR How electron mobility changes of a good conductor when temperature of the conductor decreased at (i) constant potential difference (ii) applied potential difference is doubled at constant temperature. 21. Derive an expression for the torque on a rectangular coil of area A, carrying a current I and placed in a magnetic field B. 22. Draw IV characteristics of PN junction diode. Draw circuit diagram also. 23. The energy of an electron in orbit is given by En = 13.6 eV n2 . Calculate the energy required to take an electron from ground state to the first excited state. 24. Draw a graph between the frequency of incident radiation ( ) and the maximum kinetic energy of the electrons emitted from the surface of a photosensitive material state clearly how this graph can be used for finding the work function of material. 25 A galvanometer with a coil of resistance 120 shows full scale deflection for a current of 2.5 mA. How will you convert the galvanometer into an ammeter of range 0 to 7.5 A? What is the resistance of an ideal ammeter? (SECTION C) 26. Draw a graph showing variation of binding energy per nucleon with mass no. of different nuclei. Give salient features of the curve. How does this curve explain the release of energy in the process of nuclear fission and fusion. OR What is the shortest and longest wavelength present in the Lyman series of spectral lines (R = 1.1 x 107m-1). 27. (a) State Faraday s law of electromagnetic induction. (b) Explain, with the help of a suitable example, how we can show that Lenz s law is a consequence of the principle of conservation of energy. 28. i) Plot a graph showing the variation of resistivity with temperature in the case of a a) conductor b) semiconductor c)alloy such as nichrome (ii) How does one explain such behaviour, using the mathematical expression of the resistivity 29. Use Biot-Savart s law to find expression for the magnetic field due to a circular loop of radius r carrying current I at its centre. 30. (a) In what way is diffraction from each slit related to the interference pattern in a double slit experiment. (b) Two wavelengths of sodium light 590 nm and 596 nm are used, in turn to study the diffraction taking place at a single slit of aperture 2 10 4 m. The distance between the slit and the screen is 1.5 m. Calculate the separation between the positions of the first maxima of the diffraction pattern obtained in the two cases. Or State Huygen s principle. Using this principle draw a diagram to show how a plane wave front incident at the interface of the two media gets refracted when propagates from a rarer to a denser medium. Hence verify Snell s law of refraction. (SECTION D) 31. A parallel plate capacitor is charged by a battery and now battery is disconnected and a dielectric slab of dielectric constant K is inserted between the plates. How would (i) the capacitance (ii) The electric field between plates (iii) The energy stored in the capacitor, (iv) the electric charge on plates (v) potential difference between plates be affected? Justify your answer. Or (a) State Gauss s law in electrostatics. Show, with the help of a suitable example along with the figure, that the outward flux due to a point charge q , in vacuum within a closed surface, is independent of its size or shape and is given by q/ o . (b) Two parallel uniformly charged infinite plane sheets, 1 and 2 , have charge densities + and 2 respectively. Give the magnitude and direction of the net electric field at a point (i) in between the two sheets and (ii) outside near the sheet 1 . 32. With the help of a neat and labeled diagram, explain its principle, construction and working of a moving coil galvanometer, what is the function of i. Uniform radial magnetic field ii. Soft iron core, in this device Or (a) Derive an expression for the force per unit length acting on each of the two straight parallel metallic conductors carrying current in the same direction. (b) A short bar magnet placed with its axis at 30o with an external field of 800 G experiences a torque of 0.016 Nm. (i) What is the magnetic moment of the magnet? (ii) What is the work done in moving it from its most stable to most unstable position? 33. (i) Draw a schematic labelled ray diagram of a reflecting type telescope. (ii) Write two important advantage justifying why reflecting type telescopes are prefer over refracting telescopes. (iii) The objective of a telescope is of large focal length and of larger aperture (compared to the eyepiece). Why? Give reasons. Or i)Define the term critical angle for a pair of media. A point source of monochromatic light S is kept at the centre of the bottom of a cylinder of radius 15.0 cm. the cylinder contains water (refractive index 4/3) to a heightof 7.0 cm. Draw the ray diagram and calculate the area of water surface through which the light emerges in air. ii). Designed prisms make use of total internal reflection to obtain inverted image of the object by deviating rays (i) through 90 and (ii) through 180 . (SECTION E) 34. Optical instruments are the devices which process light waves to enhance an image for a more clear view. The optical microscope is of two types: a simple microscope and a compound microscope. An optical microscope uses a single lens or a group of lenses for magnification. Q1: What is the ratio of resolving power of an optical microscope for wavelengths 1= 6000 and 2= 9000 ? Q2: Two identical glass ( g=3/2) equi convex lenses of focal length f each are kept in contact. The space between the two lenses is filled with water (( w=4/3). The focal length of the combination is Q3: What is the use of compound microscope? Q4: Does the magnification power of a compound microscope depend upon tube length. OR Why should the focal lengths of objective and eye piece of a compound microscope be small? 35. Consider a thin p-type silicon (p-Si) semiconductor wafer. By adding precisely a small quantity of pentavelent impurity, part of the p-Si wafer can be converted into n-Si. There are several processes by which a semiconductor can be formed. The wafer now contains p-region and n-region and a metallurgical junction between p-, and n- region. Two important processes occur during the formation of a p-n junction: diffusion and drift. We know that in an n-type semiconductor, the concentration of electrons (number of electrons per unit volume) is more compared to the concentration of holes. Similarly, in a p-type semiconductor, the concentration of holes is more than the concentration of electrons. During the formation of p-n junction, and due to the concentration gradient across p-, and n- sides, holes diffuse from p-side to n-side (p n) and electrons diffuse from n-side to p-side (n p). This motion of charge carries gives rise to diffusion current across the junction. (i) How can a p-type semiconductor be converted into n- type semiconductor? (ii) Which is responsible for diffusion current? (iii) What is drift current? Or How is depletion region formed? (iv) Concentration of which type of charge carrier is more in n type semiconductor? BLUE PRINT OF QUESTION PAPER UNIT NAME MCQ(1 ASSERTION 2MARKS 3MARKS MARK) & REASON(1 MARK EACH) ELECTROSTATICS 4 CURRENT ELECTRICITY 1 1 1 1 MAGNETISM&MAGNETIC 2 1 EFFECTS OF CURRENT 1 AC&EMI 1 1 EMW& 3 OPTICS 1 1 1 DUAL NATURE OF 3 1 1 MATTER &ATOMS &NUCLEI 1 1 1 SEMICONDUCTOR 1 1 DEVICES TOTAL 1 x 15 = 15 *TOTAL MARKS (NO OF QUESTIONS) 1x3=3 2 x 7 = 14 3x5= 15 5MARKS TOTAL 1 9+7 8+9 1 3+15 1 6+6 7 5 x 3 = 15 70(35) CLASS-XII TIME: 3 HOURS KENDRIYA VIDYALAY SANGATHAN, JAMMU REGION SAMPLE PAPER SET-12 SUBJECT- PHYSICS M.M. 70 General Instructions: (1) There are 35 questions in all. All questions are compulsory (2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E. All the sections are compulsory. (3) Section A contains eighteen MCQ of 1 mark each, Section B contains seven questions of two marks each, Section C contains five questions of three marks each, section D contains three long questions of five marks each and Section E contains two case study based questions of 4 marks each. (4) There is no overall choice. However, an internal choice has been provided in section B, C, D and E. You have to attempt only one of the choices in such questions. 5. Use of calculators is not allowed. SECTION A 1.For a point charge, the graph between electric field versus distance is given by : - 2. Charge Q is kept in a sphere of 5 cm first then it is kept in a cube of side 5 cm. the outgoingflux will be(a) More in case of sphere (b) More in case of cube (c) Same in both case (d) Information Incomplete 3. A cell supplies a current of 0.9 A through a 2 resistor and a current of 0.3 A through 7 resistor. The internal resistance of the cell is (a) 2.0 (b) 1.5 (c) 1.0 (d) 0.5 4. Two wires of same material have length L and 2L and cross sectional areas 4A and A respectively. The ratio of their specific resistance would be (a) 1 : 2 (b) 8:1 (c) 1 : 8 (d) 1:1 5. Two wires of same length are shaped into a square and a circle if they carry same current, ratio of magnetic moment is : (a) 2: (b) :2 (c) : 4 (d) 4 : 6. The coil of a moving coil galvanometer is wound over a metal frame in order to (a) reduce hysteresis (b) increase sensitivity (c) increase moment of inertia (d) provide electromagnetic damping 7. A metallic cylinder is held vertically and then a small magnet is dropped along its axis. Itwill fall with(a) acceleration a>g (b) acceleration a g (c) acceleration a=g (d) constant velocity a=0 8. The variation of the instantaneous current I(t) and the instantaneous emf E(t) in a circuit is as shownin the following fig. Which of the following statements is correct? (a) The voltage lags behind the current by /2 (b) The voltage leads the current by /2 (c) The voltage and the current are in phase (d) The voltage leads the current by 9. Two lenses of focal lengths 20 cm and - 40cm are held in contact. If an object lies at infinity,image formed by the lens combination will be at (a) infinity (b) 20cm (c) 40cm (d) 60cm 10. Which of the following has maximum stopping potential when metal is illuminated by visiblelight? (a) Blue (b) Yellow (c) Violet (d) Red 11. For the shortest wavelength present in the Paschen series of spectral lines (a) n2 = 3, n1 = 2 (b) n2 = , n1 = 3 (c) (d) n2 = 3, n1 = n2 = 4, n1 = 1 12. Light can travel in vacuum due to its: a) Transverse nature b) Electromagnetic Nature c) Longitudinal Nature d) Both a and c 13. An air bubble in a jar of water shines brightly is an example of : a) Total internal reflection b) Refraction c) Reflection d) Polarisation 14. During photo electric emission, when intensity of light is doubled: a) Both no. of emitted electrons and kinetic energy are doubled b) No. of emitted electrons is doubled c) Kinetic energy of emitted electrons is doubled d) No change is observed 15. When an electron jumps from 2nd stationary orbit of hydrogen atom to 1st stationary orbit, theenergy emitted is: a) mc2 b) h c) h /c d) hc/ Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect. 16. Assertion: To convert a galvanometer into an ammeter a small resistance is connected in parallel with it. Reason: The small resistance increases the combined resistance of the combination. 17. Assertion : If the rays are diverging after emerging from a lens; the lens must be concave. Reason : The convex lens can give diverging rays. 18. Assertion : Density of all the nuclei is same. Reason : Radius of nucleus is directly proportional to the cube root of mass number. 19. SECTION B Two charges each 2 x C but opposite in sign forms a system. These charges are located at points A (0,0, -10) cm and B(0,0, +10) cm respectively. What is the total charge and electric dipole moment of the system? 10-7 Two materials Si and Cu, are cooled from 300 K to 60 K. Show graphically the effect on their resistivity? A narrow beam of protons and deuterons, each having the same momentum, enters a region of uniform magnetic field directed perpendicular to their direction of momentum. What would be the ratio of the circular paths described by them? OR A circular coil of N turns and diameter d carries a current I . It is unwound and rewound to make another coil of diameter 2d , current I remaining the same. Calculate the ratio of the magnetic moments of the new coil and the original coil. 22. Two identical loops, one of copper and another of aluminum are rotated with the same speed in the same magnetic field. In which cases i) The induced emf ii) The induced current, will be more and why? 23. The oscillating magnetic field in a plane electromagnetic wave is given by By =(8 X 10-6 ) sin [2 X 1011t + 300 x ]T (i) Calculate the wavelength of the electromagnetic wave. (ii) Write down the expression for the oscillating electric field. 24. The energy level diagram of an element is given below. Identify, by doing necessary calculations for each , which transition corresponds to the emission of a spectral line of wavelength 102.7 nm. 20. 21. OR Show that nuclear density in a given nucleus is independent of mass number A. 25. A semiconductor has equal electron and whole concentration of 6X10 8 / m3 . On doping with certain impurity, electron concentration increases to 8X1012 / m3 . (i) Identify the new semiconductor (ii) Calculate the new whole concentration. SECTION- C 26. Draw a labelled diagram of a moving coil galvanometer and explain its working. What is the function of radial magnetic field inside the coil? OR A closely wound solenoid of 2000 turns and area of cross-section 1.6x10 4 m 2 carrying current of 4.0A is suspended through its centre allowing it to turn in a horizontal plane. a. What is the magnetic moment associated with the solenoid? b. What is the force and torque on the solenoid if a uniform horizontal magnetic field of 7.5x10 2 T is set up at an angle of 30 0 with the axis of the solenoid? 27. You are given three lenses L1, L2 and L3 each of focal length 20 cm. An object is kept at 40 cm in front of L1, as shown. The final real image is formed at the focus I of L3. Find the separations between L1, L2 and L3. 28. Calculate the binding energy of an particle in MeV, given that: mp= 1.007825 amu; mn = 1.008665 amu; Mass of helium nucleus He = 4.002800 amu and 1 amu = 931 MeV 29. Derive the expression for the electric field intensity at any point on the equatorial line of an electric dipole ? OR Calculate the amount of work done in rotating a dipole, of dipole moment 3 X10-8 C-m, from its position of stable equilibrium to the position of unstable equilibrium, in a uniform electric field of intensity 10 4 N/C. 30. Sketch a graph b/w angle of incident radiation and stopping potential for a given photosensitive material. What information can be drawn from the value of intercept on the potential axis. SECTION D 31. a) Using Gauss law, derive an expression for the electric field intensity at any point outside a uniformly charged thin spherical shell of radius R and charge density C/m 2 . Draw the field lines when the charge density of the sphere is (i) positive, (ii) negative. (b) A uniformly charged conducting sphere of 2.5 m in diameter has a surface charge density of 100 mC/m 2 . Calculate the (i) charge on the sphere (ii) total electric flux passing through the sphere. OR Derive the expression for the energy stored in a parallel plate capacitor of capacitance C with air as medium between its plates having charges Q and Q. Show that this energy can be expressed in terms of electric field as 1/2 0E2Ad, where A is the area of each plate and d is the separation between the plates. How will the energy stored in a fully charged capacitor change when the separation between the plates is doubled and the dielectric medium of dielectric constant 4 is introduced between the plates(when battery remains connected) 32. Draw a neat and labelled ray diagram of a compound microscope when image is formed at least distance of distinct vision. (b) Derive an expression for its magnifying power. (c) Why is objective of a microscope of short aperture and short focal length? Give reason. OR What is the effect on the interference fringes to a Young s double slit experiment when (i) the separation between the two slits is decreased? (ii) the width of a source slit is increased? (iii) the monochromatic source is replaced by a source of white light? Justify your answer in each case. (c) The intensity at the central maxima in Young s double slit experimental set-up is I0. Show that the intensity at a point where the path difference is /3 is I0/4. 33. An ac source of voltage V = Vo sin wt is connected to a series combination of L, C and R. Use the phasor diagram to obtain the expression for impedance of the circuit and phase angle between voltage and current. Find the condition when current will be in phase with the voltage. What is the circuit in this condition called? b) In a series LR circuit, XL= R and power factor of the circuit is P1. When capacitor with capacitance C is connected in series to LR such that XL = XC, the power factor becomes P2. Calculate P1/P2. OR Draw a labelled diagram of step down transformer. State the principle of its working. b) Express the turn ratio in term of voltages. c) Express the turn ratio of primary and secondary currents in terms of turn ratio in an ideal transformer. d) How much current is drawn by the primary of a transformer connected to 220V supply when it delivers power to a 110V 550W refrigerator? SECTION-E(CASE STUDY QUESTIONS) 34. TOTAL INTERNAL REFLECTION When a ray of light travels from denser medium to rarer medium then it get bended away from the normal. If we increase the angle of incidence slowly then angle of refraction also get increased and at one stage the angle of refraction is 90 for some angle of incidence. And further if we increase the angle of incidence then there will be no refraction of light and the ray will be totally internally get reflected. Such phenomenon of reflection of light is called as total internal reflection of light. And the angle of incidence in denser medium for which the angle of refraction in rarer medium is 90 , that angle of incidence is called as critical angle. So we define total internal reflection as, if the angle of incidence exceeds the critical angle then the total light get internally reflected. Mirage is the best real life example of total internal reflection of light. The highly brilliance of diamonds is only due to the total internal reflection of light through them which is get total internally reflected many times and causes brilliance of diamonds. Prisms are also made by using total internal reflection of light. We all know that, optics is the vast branch of physics which has vast application in our daily life such as optical fibre. Optical fibre are used for long distance transmission of audio and video signal also. And they are mainly constructed on the basis of total internal reflection of light to reduce the decrease in amplitude of the sending signal. I) If angle of incidence is equal to critical angle then what is the value of angle of refraction. II) What is the effect on the value of critical angle as we increase the refractive index of medium. III) Write any necessary condition for total internal reflection. IV) What is mean by optically denser and optically rarer medium? 35. SEMICONDUCTORS: The semiconductors are classified as intrinsic semiconductors and extrinsic semiconductors also. Intrinsic semiconductors are those semiconductors which exist in pure form. And intrinsic semiconductors has number of free electron is equal to number of holes. The semiconductors doped with some impurity in order to increase its conductivity are called as extrinsic semiconductors. Two types of dopants are used they are trivalent impurity and pentavalent impurity also. The extrinsic semiconductors doped with pentavalent impurity like Arsenic, Antimony, Phosphorus etc are called as n type semiconductors. In n type semiconductors electrons are the majority charge carriers and holes are the minority charge carriers. When trivalent impurity is like Indium, Boron, Aluminium etc are added to extrinsic semiconductors then p type semiconductors will be formed. In p type semiconductors holes are majority charge carriers and electrons are the minority charge carriers. Questions: I) Which type of carriers have more number density in p-type semiconductor II) How is intrinsic semi-conductor behave at T = 0K III) How does a material behave if energy band gap Eg > 3eV IV) What is energy band gap in case of materials? KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -13 CLASS : XII SUBJECT: PHYSICS TIME: 3 hrs M.M: 70 General Instructions: (1) There are 35 questions in all. All questions are compulsory (2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E. All the sections are compulsory. (3) Section A contains eighteen MCQ of 1 mark each, Section B contains seven questions of two marks each, Section C contains five questions of three marks each, section D contains three long questions of five marks each and Section E contains two case study based questions of 4 marks each. (4) There is no overall choice. However, an internal choice has been provided in section B, C, D and E. You have to attempt only one of the choices in such questions. (5) Use of calculators is not allowed. SECTION A 1. When air is replaced by a dielectric medium of constant k, the maximum force of attraction between two charges separated by a distance (a) Decreases k times (b)Remains unchanged (c) Increases k times 2. 3. (d) Increases k -1 times Two point charges +2C and +6C repel each other with a force of 12 newton. If a charge of 4C is given to each of these charges the force now is (a)Zero (b) 4 N (attractive) (c)12 N (attractive) (d) 8 N (repulsive) A capacitor is kept connected to the battery and a dielectric slab is inserted between the plates. During this process (a) No work is done (b) Work is done at the cost of the energy already stored in the capacitor before the slab is inserted (c) Work is done at the cost of the battery (d) Work is done at the cost of both the capacitor and the battery 4. A parallel plate air capacitor is given a charge of 3 C. A sheet of dielectric constant 3 is inserted so that it completely fills the gap between the plates. Find the induced charge on each face of the sheet. (a) 2 c (b) 3 c (c) 4 c (d) 5 C 5. Two wire of the same material have lengths I and 2l and areas of cross section 4A and A respectively. The ratio of their specific resistance would be (a)1:2 (b)8:1 (c)1:8 (d) 1:1 These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses. (a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion. (b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion. (c) If the Assertion is correct but Reason is incorrect. (d) If both the Assertion and Reason are incorrect. 6. 7. 8. 9. 10. Assertion- The average time of collision decreases with increasing temperature. Reason-At increased temperature average speed of the electrons, which act as the carrier of current increases resulting in more frequent collision Assertion- Magnetic field cannot change kinetic energy of moving charge. Reason-Magnetic field cannot change velocity vector Assertion:- A magnetic material looses its property on heating Reason:- Diamagnetic material convert into paramagnetic substance Name the part of electromagnetic spectrum whose wavelength lies in the range of 1010 m. (a)Ultraviolet rays (b) Infrared rays (c)X-rays (d) Radio waves Which of the following waves have the maximum wavelength (a) X-rays (b) I.R. rays (c) UV rays (d) Radio waves 11. If E and B are the electric and magnetic field vectors of e.m. waves then the direction of propagation of e.m. wave is along the direction of (a) E (b) B (c) E B (d) B E 12. The strength of photoelectric current depends upon : (a) angle of incident radiation (b) frequency of incident radiation (c) intensity of incident radiation (d) distance between anode and cathode 13. In photoelectric effect, electrons are ejected from metals, if the incident light has a certain minimum (a) wavelength (b) frequency (c) amplitude (d) angle of incidence 14. What will be the de-Broglie wavelength of an electron accelerated from rest through a potential difference of 100 volts? (a) 12.3 (b) 1.23 (c)0.123 (d) None of these 15. The stopping potential in an experiment on photoelectric effect is 1.5 V. What is the maximum kinetic energy of the photoelectrons emitted? 16. The electron, in a given Bohr orbit has a total energy of -1.5 eV. Calculate its Kinetic Energy. (a) -1.5 ev (b) + 1.5 ev (c) 15 ev (d) -15 ev 17. In a p-type semiconductor, current conduction is by: (a) atoms (b) holes (c) electrons (d) protons 18. The angle of minimum deviation for an equilateral glass prism is 30 . Refractive index of the prism is: (a) 1/ 3 (b) 2 (c) 1 (d) can t be determined SECTION B 19. Two cells of E.M.F. 10 V and 2 V and internal resistances 10 and 5 respectively, are connected in parallel as shown. Find the effective voltage across R. 20. If a Proton and an Alpha particle enter a uniform magnetic field normally with the same K.E. Find the ratio of their radii. 21. State characteristic properties distinguishing the behaviour of paramagnetic, diamagnetic and ferromagnetic materials. 22. The following graph shows the variation of stopping potential Vs with frequency ( ) of the incident radiation for two photosensitive metal X and Y. a) Which of the metal has larger threshold wavelength give reason? b) Explain giving reason which metal gives out electron having larger kinetic energy for the same wavelength of the incident radiation. 23. Calculate mass defect and binding energy of 10Ne20, Given OR Explain Nuclear fission and fusion by drawing binding energy curve. 24. Explain the formation of depletion region for p-n junction diode with the help of suitable diagram. Or What is barrier potential in PN junction diode . Explain its variation with forward and reverse biase. 25. A ray of light passing through an equilateral triangular glass prism from air undergoes minimum deviation when angle of incidence is 3/4th of the angle of prism. Calculate the speed of light in the prism. SECTION C 26. A capacitor of unknown capacitance is connected across a battery of V volts. The charge stored in it is 360 C. When potential across the capacitor is reduced by 120 V, the charge stored in it becomes 120 C.Calculate: (i) The potential V and the unknown capacitance C. (ii) What will be the charge stored in the capacitor, if the voltage applied had increased by 120 V? OR A hollow cylindrical box of length 1 m and area of cross-section 25 cm2 is placed in a three dimensional coordinate system as shown in the figure. The electric field in the region is given , where E is NC 1 and x is in metres. Find (i) Net flux through the cylinder. (ii) Charge enclosed by the cylinder. 27. Two long straight parallel conductors carry steady current I1 and I2 separated by a distance d. If the currents are flowing in the same direction, show how the magnetic field set up in one produces an attractive force on the other. Obtain the expression for this force. Hence define one ampere. 28. Define Mutual inductance and give its SI unit. Derive an expression for the mutual inductance of two circular loops with radius R1 and R2 such that R1 is greater than R2. OR Ddefine self inductance. Give its SI units. Derive an expression for self inductance for a long straight solenoid of length L and area of cross section A having N number of turns. 29. (i) Find the ratio between the wavelengths of the most energetic spectral lines in the Balmer and Paschen series of the hydrogen spectrum. (ii) Name the series of hydrogen spectrum which lies in the visible region. 30. State Huygen s principle. Using Huygen s construction draw a figure showing the propagation of a plane wave refracting at the inter face of the two media. Hence verify Snell s law of refraction. SECTION D 31. Two isolated metal spheres A and B have radii R and 2R respectively, and same charge q. (a) Find which of the two spheres have greater : (i) Capacitance and (ii) energy density just outside the surface of the spheres. (b) (i) Show that the equipotential surfaces are closed together in the regions of strong field and far apart in the regions of weak field. Draw equipotential surfaces for an electric dipole. (ii) Concentric equipotential surfaces due to a charged body placed at the centre are shown. Identify the polarity of the charge and draw the electric field lines due to it. OR (a) Compare the individual dipole moment and the specimen dipole moment for H2O molecule and O2 molecule when placed in (i) Absence of external electric field (ii) Presence of external electric field. Justify your answer. (b) Given two parallel conducting plates of area A and charge densities + & - . A dielectric slab of constant K and a conducting slab of thickness d each are inserted in between them as shown. (i) Find the potential difference between the plates. (ii) Plot E versus x graph, taking x=0 at positive plate and x=5d at negative plate. 32. i) An a.c. source of voltage V = V0 sin wt is connected to a series combination of L, C and R. Use the phasor diagram to obtain expressions for impedance of the circuit and phase angle between voltage and current. Find the condition when current will be in phase with the voltage. What is the circuit in this condition called? (ii) What is power factor? (iii) What is wattles current? OR i) Write the function of a transformer. State its principle of working with the help of a diagram. Mention various energy losses in this device. (ii) The primary coil of an ideal step up transformer has 100 turns and transformation ratio is also 100. The input voltage and power are respectively 220 V and 1100 W. Calculate (a) number of turns in secondary (b) current in primary (c) voltage across secondary (d) current in secondary (e) power in secondary 33. Draw a ray diagram of a telescope in the position, when the image is formed at least distance of distinct vision D . Write the expression for its angular magnification. A small telescope has an objective lens of focal length 140 cm and an eye piece of focal length 5 cm .What is a) magnifying power at normal adjustment, b) Sepration between the objective and eyepiece? OR (a) Draw a ray diagram for the image formation by a compound microscope, when the image is formed at least distance of distinct vision D . Write the expression for its angular magnification. (b) A compound microscope uses an objective of focal length 4 cm and eyepiece of focal length 10 cm. An object is placed at 6 cm from the objective lens. Calculate magnifyingpowerof microscope and length of the microscope. SECTION E 34. CASE STUDY: p-n junction P-n junction is the key to all semiconductor devices. When such a junction is made, a depletion layer is formed consisting of immobile ion-cores devoid of their electrons or holes. This is responsible for a junction potential barrier. By changing the external applied voltage, junction barrier can be changed. In forward bias, the barrier is decreased while the barrier increases in reverse bias. Hence, forward bias current is more (mA) while it is very small ( A) in reverse biased junction diode. The given figure shows a germanium semiconductor device. (Answer any four of the following questions) I. In the diagram, section A represents the II. III. IV. What is the bias of the p-junction shown in the diagram. In the diagram, section B represents the Where is the depletion layer formed. CASE STUDY: Interference (Young s double slit experiment) (Answer any four of the following questions) I) What is the path difference between the two light waves coming from coherent sources, which produces 3rd maxima? II) What is the correct expression for fringe width( ). III) what is the phase diff. between two interfering waves producing 1st dark fringe. IV) The ratio of the widths of two slits in Young s double slit experiment is 4 : 1. Evaluate the ratio of intensities at maxima and minima in the interference pattern. OR In a Young s double slit experiment, the separation between the slits is 0.1 mm, the wavelength of light used is 600 nm and the interference pattern is observed on a screen 1m away. Find the separation between bright fringes. KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -14 CLASS : XII TIME: 3 hrs SUBJECT: PHYSICS M.M: 70 General Instructions: 1. All questions are compulsory. There are 35 questions in all. 2. This question paper has five sections: Section A, Section B, Section C, Section D and Section E. 3. Section A contains eighteen questions of one mark each, Section B contains seven questions of two marks each, Section C contains five questions of three marks each, and Section D contains two questions and section E contains three questions of five marks each. 4. There is no overall choice. However, internal choices are provided. You have to attempt only one of the choices in such questions. S.NO 1. 2. 3. MARKS Section A All questions are compulsory. In case of internal choices, attempt any one of them. What is the angle of dip at the magnetic equator? 1 0 a) 90 b) 1800 c) 450 d) 00 represent electric and Magnetic Field vectors of an EM 1 If and Wave, then what is the direction of propagation of an EM wave? a) . b) x . c) x d) A charged particle enters into a uniform magnetic field and 1 experiences an upward force as indicated in the figure. What is the nature of charge on the particle? a) Negative b) Neutral c) Positive d) Can t be determined 4. The instantaneous current in an ac circuit is i =2.0 sin 314t, what is rms value of the current. a) 1.414 A b)14.14 A c) 0.1414 A d) 0 A 1 5. The diagram shows the energy levels for an electron in a certain atom. Which transition shown represents the emission of a photon with the most energy 1 6. a) I b) II c) III d) IV The work function of a substance is 4.0 eV. What is the longest 1 wavelength of light that can cause photo-electrons emission from this substance (approximately)? a) 410 nm b) 210 nm c) 310 nm d)510 nm 7. Which series of hydrogen spectra exists in visible region? a) Lyman b) Paschen c)Brackett d) Balmer 1 8. 9. In a p- type semiconducting material, the Fermi level is 0.3 eV above 1 the valence band. The concentration of accepter atoms is increased. The new position of Fermi level is likely to be shifted towards which band? a) C.B b) V.B c) Will not shift d) Can t be determined When the voltage drop across a p-n junction diode is increased from 1 0.65V to 0.70V, the change in the diode current is 5mA. What is the dynamic resistance of the diode? a) 5 b) 10 c) 15 d) 0.5 10. 11. Where does the Fermi level lies for a p-type semiconductor? 1 a) Close to V.B b) Close to C.B c) Away from V.B d) At infinity 1 Optical fiber communication uses the principle A. B. C. D. light scattering light path reversibility Total internal reflection least action 12 The work function of a metal is hc/ 0. If light of wavelength is incident on its surface , then the essential condition for the electron to come out from the metal surface is (a) 0 (b) 2 0 (c) 0 (d) 2 0 1 13 The index of refraction of a certain glass is 1.50. The sine of the critical angle for total internal re ection at a glass-air interface is: a) 0.50 b) 0.67 c) 0.75 d) 1.00 The reason there are two stilts rather one, in a Young's experiment is : 1 14 1 (a) (b) (c) (d) 15 16. 17. 18. 19. 20. To increase the intensity One slit is for frequency, the for wavelength To create a path length difference One slit is for E fields, the other is for B fields Kirchhoff s first and second laws in the electricity are the laws 1 respectively of (a)Energy and Momentum conservation (b)Momentum and charge conservation (c)Mass and charge conservation (d)Charge and energy conservation For question numbers 16, 17 and 18, two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true but R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is also false Assertion: The electrostatic force between the plates of a charged 1 isolated capacitor decreases when dielectric fills whole space between plates. Reason: The electric field between the plates of a charged isolated capacitance increases when dielectric fills whole space between plates. Assertion: two equipotential surfaces cannot cut each other. 1 Reason: equipotential surfaces are parallel to each other. Assertion: The refractive index of diamond is 6and that of liquid 1 is 3. If the light travels from diamond to the liquid, it will totally reflected when the angle of incidence is 30 . Reason : =sinC, where is the refractive index of diamond with respect to liquid. Section B All questions are compulsory. In case of internal choices, attempt anyone. A galvanometer is first converted into a voltmeter of range 0 3V 2 and then into a voltmeter of range 0 6 V. In which case the resistance would be higher one? Why? If one of the slits in the Young s double slit experiment is painted, so 2 as to allow only half the light intensity to pass than the other, then what will be the effect on the intensity of the maxima and minima in the interference pattern? 21. 22. 23. 24. 25. 26. 27. OR The fringe width in Young s double slit interference pattern is 2.4 x 10-4 m when red light of wavelength 6400 is used. By how much will it change if blue light of wavelength 4000 is used? An electric dipole is held in a uniform electric field. 2 (i) Show that the net force acting on it is zero. (ii) The dipole is aligned parallel to the field. Find the work done in rotating it through the angle of 1800. OR What is an equi-potential surface? Show that the electric field is always directed perpendicular to an equi-potential surface. Draw circuit diagram and input and output wave forms of half wave 1, , 1,2 and full wave rectifiers. Explain, how Len z law follow law of conservation of energy. 2 In the figure given below SS1- SS2 = /4. Find the position of central 2 maxima from O if P is midpoint of S1& S2 Give two differences between p-type and n-type semiconductor. 2 How these are made from intrinsic semiconductors? Section C All questions are compulsory. In case of internal choices, attempt any one. A long straight wire of a circular cross-section of radius a carries a 3 steady current I . The current is uniformly distributed across the cross-section. Apply Ampere s circuital law to calculate the magnetic field at a point r in the region for (i) r < a and (ii) r > a. Calculate the current drawn from the battery in the given network 3 shown below. OR State Kirchhoff s rules. Use these rules to write the expressions for the currents I1 , I2 and I3 in the circuit diagram shown. 28. (I) State two important features of Einstein s Photoelectric equation. 3 (II) Radiation of frequency 1015 Hz is incident on two photosensitive surface P and Q. there is no photoemission from surface P. photoemission occurs from surface Q but photoelectrons have zero kinetic energy. Explain this observation and find the value of work function for surface Q. OR A beam of monochromatic radiation is incident on a photosensitive surface answer the following questions giving reasons : (i) 29. do the emitted photoelectrons have the same kinetic energy? (ii) does the kinetic energy of the emitted electrons depend on the intensity of incident radiation ? (iii) on what factors does the number of emitted photoelectrons depend? The value of ground state energy of hydrogen atom is -13.6 eV : 3 What does the negative sign signify? How much energy is required to take an electron in this atom from the ground state to the first excited state ? 30. Obtain the binding energy of a nitrogen nucleus from the following data mH=1.007834; mn=1.00867; mN=14.03074. Give your answer in MeV. 3 Section- D Questions 31 and 32 are Case Study based questions and are compulsory. Each sub- part carries 1 mark. 31. Transformer 3 A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another, or multiple circuits. A varying current in any one coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force across any other coils wound around the same core. Electrical energy can be transferred between separate coils without a metallic (conductive) connection between the two circuits. Transformers are most commonly used for increasing low AC voltages at high current or decreasing high AC voltages at low current in electric power applications, and for coupling the stages of signal-processing circuits. Transformers can also be used for isolation, where the voltage in equals the voltage out, with separate coils not electrically bonded to one another. 1. Why does the core of any transformer laminated? 2. Describe humming loss in a transformer. 3. Explain the working principle of transformer. 4. For an ideal-step-down transformer, name the quantity which is constant for both the coils. 32 Mirage 3 an optical phenomenon, especially in the desert or at sea, by which the image of some object appears displaced above, below, or to one side of its true position as a result of spatial variations of the index of refraction of air. 1. Mirage is caused due to the phenomenon of? 2. The Critical angle of glass is 1 and that of water is 2. The critical angle for water and glass surface would be less than 2 or greater than 2 ( g = 3/2, w = 4/3). 3. If the critical angle for total internal reflection from a medium to vacuum is 30o, what is the velocity of light in the medium? 4. Define Critical angle. 33. Section E All questions are compulsory. In case of internal choices, attempt any one. (a) Two thin infinite sheets 1 and 2 having surface charge densities + and - 2 respectively are as shown in the diagram. 5 Find the electric field at points A and B. (b) A capacitor of capacity C is charged fully by connecting it to a battery of emf E. It is then disconnected from the battery. If the separation between the plates of the capacitor is doubled then how the following parameters will change:i) Charge stored in the capacitor ii) Field strength between the plates iii) Energy stored by the capacitor OR (a) Define electric dipole. Derive an expression for the electric potential on the axial line due to an electric dipole. (b) An electric dipole of length 4cm, when placed with its axis making an angle of 60o with a uniform electric field, experiences a torque of 4 3 Nm. Calculate the potential energy of the dipole, if it has a charge of 8 . 34. 35. A series LCR circuit is connected to an ac source. Using the phasor 5 diagram, derive the expression for the impedance of the circuit. Plot a graph to show the variation of current with frequency of the source, explaining the nature of its variation and hence calculate impedance at resonance. OR (a) Define the coefficient of self-inductance. Find the coefficient of self-inductance of a long co axial solenoid. (b) A metallic rod of length l is rotated at a constant angular speed , normal to a uniform magnetic field B. Derive an expression for the current induced in the rod, if the resistance of the rod is R. (a) Derive lens maker s formula for a given biconvex lens. 5 (b) Double convex lenses are to be manufactured from a glass of refractive index 1.55 with both faces of the same radius of curvature. What is the radius of curvature required if focal length is to be 20 cm? OR (a) Draw the ray diagram of image formation by a refracting telescope when final image is formed at far point. Write the formula for its magnifying power. (b) A small telescope has an objective lens of focal length 144 cm and an eyepiece of focal length of 6 cm. Calculate its magnifying power and separation between both lenses. KENDRIYA VIDYALAYA SANGATHAN, JAMMU REGION SAMPLE PAPER SET -15 CLASS : XII SUBJECT: PHYSICS TIME: 3 hrs M.M: 70 General Instructions: (1) There are 35 questions in all. All questions are compulsory (2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E. All the sections are compulsory. (3) Section A contains eighteen MCQ of 1 mark each, Section B contains seven questions of two marks each, Section C contains five questions of three marks each, section D contains three long questions of five marks each and Section E contains two case study based questions of 4 marks each. (4) There is no overall choice. However, an internal choice has been provided in section B, C, D and E. You have to attempt only one of the choices in such questions. You may use the following values of physical constants wherever necessary. c = 3 x 108 m/s h = 6.63 x 10-34 Js e = 1.6 x 10-19 C o = 4 x 10-7 T m A-1 0 = 8.854 x 10-12 C2 N-1 m-2 1 = 9 x 109 N m2 C-2 4 me = 9.1 x 10-31 kg mass of neutron = 1.675 x 10-27 kg mass of proton = 1.673 x 10-27 kg Avogadro s number = 6.023 x 1023 per gram mole Boltzmann constant = 1.38 x 10-23 JK-1 Sr.No. 1. 2. Marks Section A All questions are compulsory. In case of internal choices, attempt any one of them. A point charge of Q is placed at the corner of a cube of side 10cm, what is the 1 magnitude of electric flux through one surface of the cube. (a) Q/24 0 (b) Q/ 0 (c) Q/8 0 (d) Q/10 0 For a given surface the Gauss s law is stated as E.ds = 0 . From this we can 1 conclude that (a) E is necessarily zero on the surface (b) E is perpendicular to the surface at every point (c) The total flux through the surface is zero (d) Both b & c are correct 3. A p-n photo diode is made of a material with a band gap of 2.0 eV. The minimum 1 frequency of the radiation that can be absorbed by the material is nearly? (a) 5 1014 Hz (b) 5 1013 Hz (c) 5 1012 Hz (d) 5 1011 Hz 4. Which rays are not the portion of electromagnetic spectrum (a) X-rays (b) Microwaves (c) -rays (d) Radio waves 5. AB is a wire of uniform resistance. The galvanometer G shows no current when the 1 length AC = 20 cm and CB = 80 cm . The resistance R is equal to R (a) 2 1 (b) 8 80 G A (c) 20 B C (d) 40 6. An electron, proton and -particle are accelerated by a same potential difference 1 which one have greater de-Broglie wavelength? (a) electron (b) proton (c) -particle (d) a and b both 7. Two protons A and B are placed in space between plates of a parallel plate capacitor 1 charged upto V volts (see fig.) Forces on protons are FA and FB , then (a) FA FB (b) F A (c) FB FA = FB + + + A B + + (d) Nothing can be said 8. Speed c of E.M. waves through vacuum is given by (a) c = 0 0 (b) 9 c= 1 0 0 Two beams of light having intensities I and 4I interfere to produce a fringe pattern 1 on a screen. The phase difference between the beams is /2 at a point A and at point B. Then the difference between the resultant intensities at A and B is (a) 2I (b) 4I (c) 5I (d) 7I 10 If E and B are the electric and magnetic field vectors of e.m. waves then the 1 direction of propagation of e.m. wave is along the direction of (a) E (b) B (c) E B (d) None of these 11. The magnetic field due to a straight conductor of uniform cross section of radius a 1 and carrying a steady current is represented by B B r (a) a 12 B (d) a (b) r B a r(c) r a A parallel plate capacitor carries a charge q. The distance between the plates is doubled by 1 application of a force. The work done by the force is (a) Zero 13 (b) q2 C (c) q2 2C (d) q2 4C The work function of caesium is 2.14eV. The threshold frequency for caesium is (a) (b) (c) (d) 14 1 5.16 x 1014Hz 2.08 x 1014 Hz 5.16 x 1013Hz 5.16 x 1010Hz In a circuit, the current lags behind the voltage by a phase difference of / 2 . The 1 circuit contains which of the following (a) Only R (b) Only L (c) Only C (d) R and C 15 Na and Cu have work function 2.3eV and 4.5eV respectively. Then the ratio of the wavelength is nearest to (a) 1:2 (b) 4:1 (c) 2:1 1 (d) 1:4 For question numbers 16, 17, and 18, two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below. a) Both A and R are true and R is the correct explanation of A b) Both A and R are true but R is NOT the correct explanation of A c) A is true but R is false d) A is false and R is also false 16 Assertion(A) : 1 In a metallic wire if we increase the temperature of wire the resistance of the wire also increases. Reason(R): on increasing the temperature thermal velocity of electrons increases and relaxation time period decreases in this way number of collision increases. 17 Assertion(A) : Photoelectric effect demonstrates the particle nature of light. 1 Reason(R): the number of photoelectrons is proportional to the frequency of light. 18 Assertion(A) : Bohr postulated that the electrons in stationary orbits around the 1 nucleus do not radiate. Reason(R): According to classical Physics, all moving electrons radiate. Section B All questions are compulsory. In case of internal choices, attempt anyone. Explain drift velocity and deduce the formula for drift velocity. Or A cell of emf E and internal resistance r draws a current Write the relation between terminal voltage V in terms of E, I and r.The emf of a cell is always greater than its terminal voltage. Why? Give reason. 2 20 State Ampere s circuital law, using this law find the expression for magnetic field due to infinite long straight wire. 2 21 Explain De Broglie s explanation of Bohr s second postulate of quantization 2 22 Explain the formation of depletion layer in p-n junction and write its importance in 2 p-n junction. 23 The two lines marked A and B in show a plot of de-Broglie 19 wavelength ( ) as a function of 1 2 (V is the accelerating potential) for two nuclei 1H and 1H3. (i) (ii) 24 What does the slope of the lines represent? Identify, which lines correspond to these nuclei? Using Huygen s principle prove refraction of light Or Using Huygen s principle explain that wavelength of light decreases when light travel from optically rare medium to optically denser medium. 2 25 Derive the expression for the force b/w two infinite long parallel current carrying 2 wire. What will be the direction of force when current are flowing in same direction in wires. Using the expression derived in above question define one Ampere current. 26. Section -C All questions are compulsory. In case of internal choices, attempt any one. A cell of emf E1 = 2V and internal resistance 1 is connected in parallel with another cell of emf E2 = 1.5V and internal resistance 2 . When the combination is in parallel with a resistance of 4 . Find the current through each branch and also the potential difference across the 4 resistor. 3 Or Using kirchhoff s laws in the given circuit calculate the values of I1, I2 and I3 . 27 28 Mangal s transformer, whose efficiency is 90% draws 5A, when 200V is applied 3 to its primary coil. Find the current in secondary coil, if output is drawn at 300V. the number of turns in the primary coil being 500 find the number of turns in secondary coil.. (i) Draw a neat labelled ray diagram of astronomical telescope. Explain briefly 3 it s working. (ii) The critical angle for glass air interface is C and for glass water interface is C . How are C and C related? 29 Explain binding energy. Draw the curve showing the variation of binding energy per nucleon with the mass number of nuclei. Using it explain the fusion of nuclei lying on ascending part and fission of nuclei lying descending part of this curve. 3 30. Deduce the magnetic field at a point on the axis of a current carying loop. Or What is Self Inductance? Obtain an expression for self inductance of a long 3 straight solenoid of area A, length & having n number of turns per unit length. Section D All questions are compulsory. In case of internal choices, attempt any one. 31 (a) Construct a refracted wave front using Huygens principle, when a plane wave 5 front is incident on a plane surface from an optically denser medium. Further with its help define critical angle and write the condition for total internal reflection. (b) The intensity at the central maxima O in Young s double slit experiment is I0. If the distance OP equals one third of fringe width of the pattern, then show that the intensity at point P would be I0 /4 ? Or (a) Find an expression for linear width of central maxima in diffraction pattern obtained from a single slit. Also draw a graph of intensity distribution pattern. (b) In our daily life we see the diffraction of sound but we never see diffraction of light explain. 32 (a) Define electric flux, write it s SI unit. (b) How can we use Gauss s theorem to determine the Electric field due to two thin infinite plane parallel sheets of charge ? (c) Show that the Electric field is independent of the distance between the infinite plane sheets of charge, if the two sheets have equal and opposite surface charge densities. 5 Or (a) Define electric dipole. Derive an expression for the electric potential on the equatorial line due to an electric dipole. (b) An electric dipole of length 4cm, when placed with its axis making an angle of 60o with a uniform electric field, experiences a torque of 4 3 Nm. Calculate the potential energy of the dipole, if it has a charge of 8 . 33 A circuit containing a 80mH inductor and a 60 F capacitor in series is connected 5 to a 230 V, 50Hz supply. The resistance of the circuit is negligible. (1) (2) (3) (4) (5) Calculate peak and rms value of current Calculate potential drop across each element of the circuit. What is the average power transferred to the inductor? What is the average power transferred to the capacitor? What is the average power absorbed by the circuit. Or (a) Draw a schematic diagram of ac generator and explain its working. Deduce the formula of induced e.m.f. in a coil of ac generator. (b) A generator has emf of 440V and internal resistance 400 . Its terminals are connected to 400 load. Find the voltage across the load. Section E Questions 34 and 35 are Case Study based questions and are compulsory. Attempt any 4 sub parts from each question. Each question carries 1 mark. 34. Mirage A mirage is a naturally occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. Under certain conditions, such as over a stretch of pavement or desert air heated by intense sunshine, the air rapidly cools with elevation and therefore increases in density and refractive power. Sunlight reflected downward from the upper portion of an object for example, the top of a camel in the desert will be directed through the cool air in the normal way. Although the light would not be seen ordinarily because of the angle, it curves upward after it enters the rarefied hot air near the ground, thus being refracted to the observer s eye as though it originated below the heated surface. A direct image of the camel is seen also because some of the reflected rays enter the eye in a straight line without being refracted. The double image seems to be that of the camel and its upsidedown reflection in water. When the sky is the object of the mirage, the land is mistaken for a lake or sheet of water. 1. For total internal reflection to take place the incident angle should be: a) greater then critical angle b) smaller then critical angle c) equal to the critical angle d) None of the above. 2. In desert mirage take place when light rays goes from: a) denser medium to rarer medium b) rarer medium to denser medium c) Both (a) and (b) d) None of the above 3. Mirage take place when there isa) Total internal reflection of light. b) Refraction of light. c) Reflection of light d) Both (a) and (b) 4 The refractive index for light of wavelength 400 nm passing through a type of glass is 1.470; when light of wavelength 750 nm passes through the glass the measured refractive index is 1.455. Which of these kinds of light travels faster in the glass 5. A pulse of white light is sent straight down a fibre optic cable 1 km long. The refractive index for blue light is 1.639 and for red light 1.621. What time interval will there be between the two components when they reach the far end? 35. Vijay was preparing an electronic project for science exhibition. He required to light the LED using a 6V supply. LEDs need only a very small current to make them light and they do not heat up in use. So he put a resistor in series to limit the current. Then, there would be potential difference of 4V across the resistor as there is always 2.0V across the LED itself when it is conducting. The current should be 10 mA through both LED and the resistor. He could use the resistance by equation R= to calculate the value of R. R= 4 = 10 4 = 0.01 = 400 Thus the protecting resistor should be around 400 1. What do you mean by semiconductor? 1 2. A semiconductor has equal electron and hole concentration 6 108 /m3. On doping with certain impurity, electron concentration increases to 9 1012 /m3. Identify the new semiconductor obtained after doping. 1 3. For the condition given above in question number 2 Calculate the new hole concentration 1 4. What are two types of charge carriers in semiconductors? 1 5. What do you mean by avalanche breakdown? 1

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