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CBSE Class 12 Sample / Model Paper 2025 : Physics

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Ezhil roja Sundaravel
Queen Mira International School, Madurai

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SET: 1 Al Sabah Indian Private School, Dhaid, Sharjah Model Assessment 1 2024 - 25 Grade: XII Subject: Physics Name of Student: Marks: 70 Roll No. Time:3 Hours Invigilator s Sign: General Instructions: 1. There are 33 questions in all. All the questions are compulsory. 2. This question paper has five sections. Section A, Section B, Section C, Section D, Section E. All the sections are compulsory. 3. Section A contains sixteen MCQs of 1 mark each, Section B contains five questions of two marks each, Section C contains seven questions of three marks each, Section D contains two Case Based Question of 4 marks each and Section E contains three questions of five marks each. 4. There is no overall choice. However, an internal choice has been provided in one question of two marks, two question of three marks and all the three questions of five marks weightage. You have to attempt only one of the choice in such questions 5. Use of a calculator is not allowed. You may use the following values of physical constants wherever necessary c = 3 108 m/s h = 6.63 10-34Js e = 1.6 10-19 C 0 = 4 10-7 T m A-1 0 = 8.854 10-12 C2 N-1 m-2 1/4 0 = 9 109 N m2 C-2 me = 9.1 10-31 kg Mass of electron = 9.1 10-31 kg Mass of neutron = 1.675 10-27 kg Mass of proton = 1.673 10-27 kg Avogadro s number = 6.023 1023 per gram mole Boltzmann constant = 1.38 10-23 JK-1 SECTION A All questions are compulsory. In case of internal choices, attempt any one of them. 1. A spherical Gaussian surface encloses a charge of 8.85 10-8C. How would the flux change, if (1) the radius of the Gaussian surface is doubled? (a) Doubled (b) No change (c) Halved (d) None of the above 1 | Page 2. An air filled parallel plate condenser has a capacity of 2pF. The separation of the plates is (1) doubled and the interspace between the plates is filled with wax. If the capacity is increased to 6pF, the dielectric constant of wax is (a) 2 3. (b) 3 (c) 4 (d) 6 The nature of parallel and antiparallel currents are (1) (a)Parallel current repels and anti-parallel current attracts (b) Parallel current attracts and anti-parallel current repels (c) Both current attract (d) Both current repel. 4. The intensity of light emerging from the two slits in Young s experiment is in the ratio 1 : 4. (1) The ratio of the intensity of the minimum to that of the consecutive maximum will be: (a) 1 : 4 5. (b) 1 : 9 (c) 1 : 16 (d) 2 : 3 Two long conductors separated by a distance d carry currents I1 and I2 in the same direction. (1) They exert a force F on each other. Now the current in one of them is increased to two times and its direction is reversed. The distance is also increased to 3d. The new value of the force between them is(a) -2F 6. (c) -2F/3 (d) -F/3 In an ac circuit, the rms value of the current, Irms, is related to the peak current I0 as (a)Irms = I0/ 7. (b) F/3 (b) Irms = I0/ 2 (c)Irms = I0 (d) Irms = 2I0 Identify the pair having highest frequency and highest wavelength EM WAVES. (a) UV rays and X- rays (1) (1) (b) Gamma rays and Microwaves. (c) Gamma rays and Radio waves. (d) Radio waves and UV rays. 8. The total energy of the electron in the ground state of a hydrogen atom is -13.6 eV. The (1) kinetic energy of the electron in the first excited state will be (a) 1.7 eV 9. (b) 3.4 eV (c) 6.8 eV (d)13.6 eV A lens behaves as a diverging lens in air (n=1) and a converging lens in water (n=1.3). (1) The refractive index of the material of the lens is 10. (a) 1< n< 1.3 (b) n> 1.3 (c) n< 1.0 (d) n=(1+1.3)/2 A single slit diffraction pattern is obtained using a beam of red light. What happens if the red light is replaced by the blue light? (a) There is no change in diffraction pattern (b) Diffraction fringes become narrower and crowded (c) Diffraction fringes become broader and farther apart (d) The diffraction pattern disappears 2 | Page (1) 11. Silicon is doped with which of the following to obtain P type semiconductor? (a) Phosphorus 12. (b) Gallium (c) Germanium (1) (d) Bismuth Ten identical cells each of potential E and internal resistance r are connected in series to form (1) a closed circuit. An ideal voltmeter connected across 3 cells will read (a) 10E 13. (b) 13E (c) 3E (d) 5E Assertion (A): Gauss's theorem is not applicable in magnetism. (1) Reason (R): Magnetic monopoles do not exist. (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 14. Assertion (A): Photosensitivity of a metal is high if its work function is small. (1) Reason (R): Work function =hf0, where f0 is the threshold frequency. (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 15. Assertion (A): For the scattering of a-particles at a large angle, only the nucleus of the atom (1) is responsible. Reason (R): Nucleus is very heavy in comparison to particles. (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): Fragments produced in the fission of 235 U are non radioactive. (1) Reason (R): The fragments have abnormally low proton to neutron ratio. (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 SECTION B All questions are compulsory. Incase of internal choices, attempt any one. 17. Explain the laws of photoelectric emission on the basis of Einstein s photoelectric equation. Write one feature of the photoelectric effect which cannot be explained on the basis of wave theory of light. 3 | Page (2) 18. State Huygens principle. Using the geometrical construction of secondary wavelets, explain (2) the refraction of a plane wavefront incident at a plane surface. Hence verify Snell s law of refraction. OR Illustrate with the help of diagrams the action of: (i) convex lens and (ii) concave mirror on a plane wavefront incident on it. 19. Derive, with the help of a diagram, the expression for the magnetic field inside a very long (2) solenoid having n turns per unit length carrying a current I. 20. Calculate the energy released in MeV in the following nuclear reaction: (2) 21. The ground state energy of hydrogen atom is 13.6 eV. If an electron makes a transition (2) 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. SECTION C All questions are compulsory. In case of internal choices, attempt any one. 22. (i) With the help of a suitable diagram, explain the formation of depletion regions in a p-n (3) junction diode. (ii) How does its width change when the junction is: (a) forward biased & (b) reverse biased? 23. A 200 F parallel plate capacitor having plate separation of 5 mm is charged by a 100 V dc (3) source. It remains connected to the source. Using an insulated handle, the distance between the plates is doubled and a dielectric slab of thickness 5 mm and dielectric constant 10 is introduced between the plates. Explain with reason, how the (a) capacitance, (b) electric field between the plates, (c) energy density of the capacitor will change ? OR (i) Deduce the expression for the potential energy of an electric dipole placed with its axis at an angle to the external field E .Hence discuss the conditions of its stable and unstable equilibrium with suitable diagram (ii) What is the geometrical shape of equipotential surfaces due to a single isolated charge? 24. Draw a ray diagram of a reflecting type telescope. (3) State two advantages of this telescope over a refracting telescope. 25. Draw the energy bands of p-type and n-type semiconductors. 4 | Page (3) Explain with a circuit diagram the working of a full wave rectifier. 26. Two similar bars, made from two different materials P and Q are placed one by one in a non (3) uniform magnetic field. It is observed that (a) the bar P tends to move from the weak to the strong field region. (b) the bar Q tends to move from the strong to the weak field region. What is the nature of the magnetic materials used for making these two bars? Explain how these materials behave when placed in a uniform magnetic field. 27. A spherical surface of radius of curvature R separates a rarer and a denser medium as (3) shown in the figure. Complete the path of the incident ray of light, showing the formation of real image. Hence derive the relation connecting object distance u , image distance v radius of curvature R and the refractive indices n1 & n2 of the media. 28. Two large charged plane sheets of charge densities and 2 C/m2 are arranged vertically (3) with a separation of d between them. Deduce expressions for the electric field at points (i) to the left of the first sheet, (ii) to the right of the second sheet, and (iii) between the two sheets. OR Derive an expression for the torque acting on an electric dipole in a uniform electric field. SECTION D Questions 29 and 30 are Case Study based questions of four marks each and are compulsory. 29. PHOTOELECTRIC EFFECT: Photoelectric emission is possible only if the incident light is in the form of packets of energy, each having a definite value, more than the work function of the metal. This shows that light is not of wave nature but of particle nature. It is due to this reason that photoelectric emission was accounted for by quantum theory of light. 5 | Page (4) Answer the questions below: (A) For a metal having a work function W0, the threshold wavelength is . What is the threshold wavelength for the metal having work function 2W0? (a) /4 (b) /2 (c) 2 (d) 4 (B) Two beams, one of red light and the other of blue light having the same intensity are incident on a metallic surface to emit photoelectrons. Which emits electrons of greater velocity? (a) Both (b) Red light (c) Blue light (d) None (C) Light of two different frequencies whose photons energies of 1eV and 2.5eV respectively, illuminate successively a metal having work function 0.5eV. The ratio of maximum speed of emitted electrons is (a)1:2 (b) 2:3 (c) 4:5 (d) 2:5 (D) The slope of graph drawn between frequency and stopping potential is (a) h/e (b) h (c) e (d)he OR (E) Four metals A , B,C and D having work functions of 2eV, 3eV, 5eV and 6eV respectively, Which metal has lower threshold wavelength for photoelectric effect? (a)A 30. (b) B (c) C (d)D ALTERNATING CURRENT: An alternating current is that whose magnitude changes continuously with time and direction reverses periodically and the current that flows with the same magnitude in same direction is direct current. 6 | Page (4) (A) In an ac circuit V(in volt) = 100 sin (100t) and I(in mA) = 100 sin(100t+ /3) . The power dissipated in the circuit is (a) 104 W (b) 10 W (c) 2.5 W (d) 5 W (B)If an ammeter is used to measure alternating current in a circuit, which value of current will it read? (a) Peak (b) rms (c) Instantaneous (d) Average (C) If T is the time period of given alternating current, then how much time it requires to reach its peak value starting from zero? (a) T (b) T/2 (c) T/4 (d) T/8 (D) What is the average value of alternating current over one complete cycle? (a) 0 (b) Io (c) Io/2 (d) Io/4 OR (E)For 220 V mains of alternating voltage, peak value will be........................... (a) 220 V (b)220/ 2 V (c) 220 2 V (d) 110 V SECTION E All questions are compulsory. In case of internal choices, attempt any one 31. i) Show, on a plot, variation of resistivity of (a) a conductor, and (b) a typical semiconductor (5) as a function of temperature. ii) Using the expression for the resistivity in terms of number density and relaxation time between the collisions, explain how resistivity in the case of a conductor increases while it decreases in a semiconductor, with the rise of temperature. OR i)Derive the bridge balance condition in a network containing four resistors. ii)Calculate the potential difference across the 4 resistor in the given electrical circuit, using Kirchhoff s rules. 32 (i) What is capacitive reactance? If an ac voltage is applied across a capacitance C, find an expression for the current I flowing in the circuit. Also show the phase relationship between current and voltage in a phasor diagram. 7 | Page (5) (ii) If the frequency of alternating current is tripled, how will it affect resistance R, inductive reactance XL and capacitive reactance XC? (iii) For a given ac circuit, differentiate between resistance, reactance and impedance. OR (i) Derive an expression for the induced emf developed when a coil of N turns, and area of cross-section A, is rotated at a constant angular speed in a uniform magnetic field B. (ii) Current in a circuit falls from 5.0A to 0.0A in 0.1s. If an average emf of 200V induced, give an estimate of the self-inductance of the circuit. (iii) Define the unit of self inductance 33. (i) Draw a labelled ray diagram to show the formation of an image by a compound microscope. Write the expression for its magnifying power. (ii) In a compound microscope, an object is placed at a distance of 1.5 cm from the objective of focal length 1.25 cm. If the eyepiece has a focal length of 5 cm and the final image is formed at the near point, estimate the magnifying power of the microscope. (iii) A concave lens made of material of refractive index n1 is kept in a medium of refractive index n2. A parallel beam of light is incident on the lens. Complete the path of rays of light emerging from the concave lens if: (a) n1> n2, (b) n1 = n2, & (c) n1< n2. OR (i) Draw a ray diagram to show the refraction of light through a glass prism. Hence obtain the relation for the angle of deviation in terms of the angle of incidence, angle of emergence and the angle of the prism. (ii) Three rays of light red (R) green (G) and blue (B) are incident on the surface of a right angled prism as shown in figure. The refractive indices for the material of the prism for red green and blue are 1.39, 1.43 and 1.47 respectively. Trace the path of the rays through the prism. Justify your answer with a suitable explanation. 8 | Page (5)

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