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CBSE Class 12 Question Bank 2022 : Physics

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KENDRIYA VIDYALAYA ARC DOOMDOOMA PHYSICS (THEORY) CLASS: XII Time allowed: 3 hrs Max.Marks:70 General Instructions: (a) All questions are compulsory (b) There are 37 questions in total. Qns. 1 to 20 carry 1 mark each. Qns. 21 to 27 carry 2 marks each, Qns. 28 to 34 carry 3 mark each and Qns. 35 to 37 carry 5 marks each. (c) There is no overall choice. However, an internal choice has been provided in one question of 2 marks, one question of 3 marks and all three questions of 5 marks each. You have to attempt only one of the given choices in such questions. (d) Use of calculators is not permitted. (e) You may use the following physical constants wherever necessary. c = 3 x 108 m s-1 h = 6.6 x 10-34 J s e = 1.6 x 10-19C o = 4 x 10-7 T m A-1 1/4 o = 9 x 109 N m2C-2 Avogadro number NA = 6.023 x 1023 mol-1 Mass of the neutron = 1.675 x 10-27 kg Boltzmann constant, k = 1.38 x 1023 J K-1 ______________________________________________________________________________________________________ 1. The electrostatic force between two charges Q1 and Q2 at separation r is given by F= K.Q1Q2 r2 . The constant K 1) 2) 3) 4) depends on the system of units only depends on the medium between the charges only depends on both the medium between the charges and the system of units is independent of both the system of units and the medium between the charges 2. On the perpendicular bisector of an electric dipole, the electric intensity E and potential V are 1) E,V both are equal to Zero 2) E and V both are not equal to Zero 3) V = 0 but E is not equal to Zero 4) E=0 but V is not equal to Zero B. Madhavi PGT Physics 3. A Parallel plate condenser is charged and disconnected from the battery. If the plates of the capacitor are moved further apart by means of insulating handles 1) The charge in the capacitor is zero 2) The capacitance becomes infinite 3) The charge in the capacitor increases 4) The voltage across the plates increases 4. Resistivity of a conductor depends upon 1) area of cross Section 2) material and temperature 3) Length 4) all 5. On increasing the resistance of the primary circuit of potentiometer, its potential gradient will 1) become more 2) become less 3) not change 4) become infinite 6. In a region, steady and uniform electric and magnetic fields are present. These two fields are parallel to Each other. A charged particle is released from rest in this region. The path of the particle will be a 1) Ellipse 2) circle 3) Helix 4) straight line 7. A current carrying loop in a uniform magnetic field experiences 1) Force only 2) Torque only 3) Both Torque and Force 4) Neither Force nor Torque 8. Earth s magnetic field always has a horizontal component except at 1) Equator 2) Magnetic pole 3) A latitude of 600 4) None of the above 9. A coil has an inductance 0.05H and 100 turns. Calculate the flux linked with it when 0.02A current is passed through it. 1) 10 wb 2) 20 wb 3) 10 micro wb 4) 20 micro wb 10. A transformer is based on the principle of 1) Mutual inductance 2) Self inductance 3) Ampere s law 4) Lenz s law 11. Electromagnetic waves are transverse in nature is evident by 1) Polarization 2) Interference 3) Reflection 4) Diffraction 12. Rising and setting of the sun appears to be reddish because of 1) Reflection 2) Refraction 3) Total internal reflection 4) Scattering due to dust particles and air molecules 13) Nature of wave front depends on 1) Shape of source 2) distance of source 3) both 1 and 2 4) none of the above 14) The work function of a metal is 4.2eV. Two photons of each energy 2.5eV each strike an electron of the metal. Then 1) the electron emitted with zero energy 2) electron is not emitted 3) electron is emitted with increased energy 4) none of the above B. Madhavi PGT Physics 15) The wavelength of matter waves does not depend on 1) Momentum 2) Velocity 3) mass 4) charge 16) The ground state energy of hydrogen atom is 13.6eV. The kinetic energy of the electron in this state is 1) 1.85 eV 2) 13.6 eV 3) 6.8eV 4) 3.4eV 4 17) The approximate ratio of nuclear mass densities of 2 He and 6C12 1) 3 2) 4 3) 1 4) 2 3) at any temperature 4) very low temperature 18) Fusion reaction is initiated with the help of 1) low temperature 2) high temperature 19) An n-type semi conductor can be formed by doping Si or Ge with 1) III group element 2) IV group elements 3) V group elements 4) VI group elements 20) The neutral region formed at P-n junction due to recombination of electrons and holes is 1) Fermi layer 2) Depletion layer 3) Acceptor layer 21. Establish the relation between current and drift velocity? 4) All the above (2M) 22. A compass needle, pivoted about the horizontal axis and free to move in the magnetic meridian, is observed to point along the (i) Vertical direction at a place A. (ii) Horizontal direction at a place B Give the value of the angle of dip at the two places. State the orientation of the magnetic field of the earth at these two places. (2M) 23. Two Polaroid s are perpendicular to each other, and the transmitted intensity is zero. What happens to the intensity of transmitted light when one more Polaroid is placed between these two bisecting the angle between them? Take the incident beam intensity as I0. 2 (M) 24. The work function of cesium metal is 2.14 eV. When light of frequency 6x1014 Hz is incident on the metal surface, photo emission of electrons occurs. What is the a) Maximum kinetic energy of emitted electrons, b) Stopping potential. (2M) 25. Prove that the radius of the nth Bohr orbit of an atom is directly proportional to n2, where n is the principal quantum number. (2M) OR Calculate the half life of a radioactive substance if its activity drops to (1/16)th of its initial value in 30 years. (2M) 26. Identify the part of the electromagnetic spectrum which is: i) Suitable for RADAR systems, used in aircraft navigation ii) Adjacent to the low frequency end of the electromagnetic Spectrum iii) Produced in Nuclear reactions Produced by bombarding a metal target by high speed electrons. (2M) 27. The figure shows the variation of V and I vs. t for a circuit element connected to A.C mains. Name the circuit element and the phase relation between current and voltage. (2M) 28. A capacitor is charged from a battery. Assuming that the capacitor is disconnected from the charging battery, explain how; a) The capacitance, b) p. d. across the plates and c) Energy stored in the capacitor change, when a medium of dielectric constant `k is introduced between the plates. 29. (3M) Define Electric flux. What is its S.I. Unit? A student is asked to calculate the ratio of electric flux through the surfaces of spheres S1 and S2 with charges placed inside, as shown in the figure. He gets the answer as 4: 1. Check the correctness of the answer by actually calculating the electric flux ratio through the two surfaces and state whether his answer is correct or incorrect. (3M) B. Madhavi PGT Physics 30. The potentiometer wire of length 1 m is connected to a standard cell E1. Another cell E2 of e m f 1.02V is connected as shown in the circuit diagram with a resistance `r and a switch S. With the switch S open null position is obtained at a distance of 51 cm from P. Calculate (i) potential gradient of the wire and (ii) e m f of the cell E1. (iii) When the switch S is closed, will null point move towards P or towards Q? Give reason for your answer. (3M) 31. A metallic square loop ABCD of size 15cm and negligible resistance is moved at a uniform velocity of v m/s in a uniform magnetic field of 2T. The field lines being normal to the plane of the paper. The loop is connected to an electrical network of resistances each of resistance 2 . Calculate the speed of the loop for which 1mA current flows in the loop? (3M) 32. What is total internal reflection? What are the conditions under which this takes place? Discuss two important applications of this phenomenon. ( 3M) 33. The total energy of an electron in the first excited state of the hydrogen atom is about 3.4 eV. (a) What is the kinetic energy of the electron in this state? (b) What is the potential energy of the electron in this state? (c) Which of the answers above would change if the choice of the zero of potential energy is changed? (3M) B. Madhavi PGT Physics 34. What is the effect on the interference fringes in a Young s double slit experiment due to each of the following operations. a) The screen is moved away from the plane of the slits: b) The (monochromatic) source is replaced by another (monochromatic) source of shorter wavelength: c) The separation between the two slits is increased. (3M) OR What is diffraction of light? Draw a graph showing the variation of Intensity with angle in a single slit diffraction experiment. Write one feature which distinguishes the observed pattern from the double slit interference pattern. 35. Draw a schematic sketch of a cyclotron. Explain briefly how it works and how it is used to accelerate the charged particles. i) Show that time period of ions in a cyclotron is independent of both the speed and radius of circular path. ii) Write any two applications of cyclotron. (5M) OR With the help of a neat and labeled diagram, explain the underlying principle and working of moving coil galvanometer. Explain the terms current sensitivity and voltage sensitivity of galvanometer. Increasing the current sensitivity may not necessarily increase the voltage sensitivity of a galvanometer . Justify this statement. (5M)

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