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PHYSICS PAPER 1 (THEORY) Maximum Marks: 70 Time Allowed: Three hours (Candidates are allowed additional 15 minutes for only reading the paper. They must NOT start writing during this time). This paper is divided into four sections A, B, C and D. Answer all questions. Section A consists of one question having sub-parts of one mark each. Section B consists of seven questions of two marks each. Section C consists of nine questions of three marks each, and Section D consists of three questions of five marks each. Internal choices have been provided in two questions each in Section B, Section C and Section D. All working, including rough work, should be done on the same sheet as and adjacent to the rest of the answer. Answers to sub parts of the same question must be given in one place only. A list of useful physical constants is given at the end of this paper. A simple scientific calculator without a programmable memory may be used for calculations. SECTION A 14 MARKS Question 1: (A) In questions (i) to (vii) below, choose the correct alternative (a), (b), (c) or (d) for each of the questions given below: (i) Two point charges (+e) and (-e) are kept inside a large metallic cube without touching its sides. Electric flux emerging out of the cube is: (a) e / (c) - e / (d) Zero. (b) 2 e / (ii) In parallel combination of resistors: (a) current remains same (c) current and voltage both remains same (b) voltage remains same (d) none of the above. (iii) A circular coil carrying a current I has radius R and number of turns N. If all the three,i.e., the current I, radius R and number of turns N are doubled, then magnetic field at its centre becomes: (a) double (c) four times (b) half (d) one fourth. (iv) An object is kept on the principal axis of a concave mirror of focal length 10 cm, at a distance of 15 cm from its pole. The image formed by the mirror is: (a) virtual and magnified (c) real and magnified (b) vitual and diminished (d) real and diminished. (v) In Young s double slit experiment, sodium lamp is replaced by a blue light lamp. Then fringe width will become: (a) brighter (c) wider (increase) (b) fainter (d) narrower (decrease) (vi) Electric conduction in semiconductors is due to: (a) electrons (d) neither electrons nor holes. (b) holes (c) both electrons and holes (vii) Which one of the following graphs in figure represents variation of de-Broglie wavelength ( ) of a particle having linear momentum p: (B) Answer the following questions briefly: (i) How much work is done in taking an electron around a nucleus in a circular path? (ii) A wire of resistivity is stretched uniformly so that its length become four times. What is the new resistivity (Assume temperature of the wire remains constant during stretching of the wire). (iii) How does the self-inductance of a coil depend on the number of turns of the coil. (iv) A monochromatic ray of light falls on a regular prism under minimum deviation condition. What is the relation between angle of incidence and angle of emergence? (v) What is the shape of wavefront diverging from a point source of light? (vi) Name the series in the hydrogen spectrum whose few lines lie in the visible region. (vii) What is the order of energy gap in a semiconductor? SECTION B 14 MARKS Question 2: (i) Two point charges of 10 C each are kept at a distance of 3 m in vacuum. Calculate their electrostatic potential energy. OR (ii) Maximum torque acting on an electric dipole of moment 3 10 29 Cm in a uniform electric field E is 6 10 25 Nm. Find E. Question 3: A battery of emf 10 V and internal resistance 3 is connected to a resistor. If the current in the circuit is 0.5 A, what is the resistance of the resistor? What is the terminal voltage of the battery when the circuit is closed? Question 4: (i) An electron, moving with a velocity of 5 107 ms-1, enters a magnetic field of 1 Wbm-2 at an angle of 30 . Calculate the force on the electron. OR (ii) State two factors on which the sensitivity of a moving coil galvanometer depends. Question 5: What is motional emf? State any two factors on which it depends. Question 6: Name the part of the electromagnetic spectrum which is: (i) suitable for radar systems used in aircraft navigation. (ii) produced by bombarding a metal target with high speed electrons. Question 7: Fraunhofer diffraction from a single slit of width 1.24 10 6 m is observed with light of wavelength 6200 . Calculate the angular width of central maximum. Question 8: With reference to a semiconductor diode what is meant by (a) forward bias (b) depletion region? SECTION C 27 MARKS Question 9: Find the capacitance of the combination shown in the following figure in left side and find the charge on 5 capacitor. Question 10: (i) A potentiometer arrangement used to measure the emf of a cell 1 is shown above in right side. AB is the potentiometer wire of length 100 cm and the resistance 5 . The emf of a standard d.c. source (E) is 6 V and rheostat R is adjusted to 5 . If the null point is obtained at C with AC = 75 cm then find the emf of 1 . OR (ii) Draw a labeled circuit diagram of a potentiometer to compare emfs of two cells. Write the working formula. (no derivation) Question 11: Explain Ampere s circuital law. Using this law deduce the expression for magnetic field due to a infinitely long current carrying conductor. Question 12: When two thin lenses of focal lengths 1 and 2 are kept in coaxial contact, prove that their combined 1 1 1 focal length F is given by: = + . 1 2 Question 13: (i) Draw a neat labeled ray diagram showing the formation of an image at the least distance of distinct vision D by a simple microscope. When the final image is at D , derive an expression for its magnifying power at D. OR (ii) In a compound microscope consists of two convex lenses of focal lengths 1.5 cm and 5 cm. When an object is kept at a distance of 1.6 cm from the objective, the final image is formed at the least distance of distinct vision (D = 25 cm). Calculate the magnifying power of the compound microscope in this set up. Question 14: Draw a neat labeled diagram of Young s double slit experiment. Show that = where the terms have their usual meaning (either for bright or dark fringe). Question 15: The work function of cesium metal is 2.14 eV. When light of frequency 6 1014 Hz is incident on the metal surface, photoemission of electrons occurs. What is the (a) maximum kinetic energy of the emitted electrons? (b) stopping potential and (c) maximum speed of the emitted photoelectrons? Question 16: On the basis of Bohr s theory, derive the expression for the radius of the nth orbit of an electron of hydrogen atom. Question 17: Draw the circuit diagram of a full wave rectifier and explain its working. Draw the input and output waveforms. SECTION D 15 MARKS Question 18: (i) (a) A rectangular coil of area 50 cm2 and 100 turns is placed perpendicular to a magnetic field of 10 2 Wbm-2. If the coil is withdrawn from the field in 40 ms, calculate the induced emf. (b) A coil has self-inductance of 0.05 henry. Find magnitude of the emf induced in it when the current flowing through it changing at the rate of 100 As-1. OR (ii) An alternating emf of 220 V is applied to a circuit containing a resistor R having resistance of 160 and a capacitor C in series. The current is found to lead the supply voltage by an angle 3 = 1 (4). (I) Calculate: (1) the capacitive reactance (2) impedance of the circuit (3) current flowing in the circuit. (II) if the frequency of the applied emf is 50 Hz, what is the value of the capacitance of the capacitor C ? Question 19: (i) (a) Write one balanced equation each to show (1) Nuclear fission (2) Nuclear fusion (3) Emission of i.e. a negative particle. (b) In photo electric effect what is meant by the terms: (1) work function (2) stopping potential? OR (ii) (a) Alpha particles having kinetic energy 1.8 MeV each are incident on a thin gold foil, from a large distance. Applying the principle of conservation of energy, find the closest distance of approach of the alpha particle from the gold nucleus. Atomic no of gold is 79. (b) In a nuclear reactor, what is the function of (1) the moderator (2) the control rod. Question 20: Read the passage given below and answer the questions that follow: Optical instruments are of great utility. They help us in studying very tiny objects as well as very large heavenly bodies. Scientists have developed microscopes like electron microscopes which aid in studying tiny molecules of matter. They have also devised giant telescopes like Hubble telescope and James Web Space telescope which have enabled us to view distant galaxies hitherto unknown. (i) Which optical instrument is used to study detailed structure of a virus? (ii) What is the ability of an instrument to form an enlarged image of an object called? (iii) Hubble telescope orbits around the earth like a satellite. What is the advantage of such a telescope over a similar one on earth s surface? (iv) An astronomical telescope consists of two convex lenses having focal length of 200cm and 4cm. When it forms final image at infinity, calculate its (a) Magnifying power (b) Length. _______________________________________________________________________________________ Useful Constants & Relations: 1. 2. 3. 4. 5. Permittivity of vacuum Constant for Coulomb s law (1/4 ) Constant in Magnetism ( /4 ) Elementary charge e Planck s constant (h) 8 85 10 12F/m 9 109 m/F 1 10 7H/m 1.6 10 19 C 6.63 10 34 Js
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