Physics Class XII

Question 1. Give a reason to show that microwaves are better carriers of signals for long range transmission than radio waves. (1 mark)

Question 2. How does the energy gap in an intrinsic semiconductor vary, when doped with a pentavalent impurity ? (1 mark)

Question 3. State the condition in which terminal voltage across a secondary cell is equal to its e.m.f (1 mark)

Question 4. Draw an equipotential surface in a uniform electric field. (1 mark)

Question 5. If the number of turns of a solenoid is doubled, keeping the other factors constant, how does the self-inductance of the solenoid change ? (1 mark)

Question 6. What is the ration of solar constants on the surfaces of two planets, whose surface temperatures are in the ratio 1 :2 ? (1 mark)

Question 7. The wavelength of light coming from a distant galaxy is red-shifted. Is the galaxy receding or approaching the earth ? (1 mark)

Question 8. What is the angle of dip at a place where the horizontal and vertical components of earth's magnetic field are equal ? (1 mark)

Question 9. Briefly explain how the distance of an inferior planet from earth can be determined ? (2 marks)

Question 10. Using Gauss' law, show that no electric field intensity exists inside a hollow charged conductor. (2 marks)

Question 11. Define the terms 'threshold frequency' and 'stopping potential' for photo-electric effect. Show graphically how the stopping potential, for a given metal, varies with frequency of the incident radiations. Mark threshold frequency on this graph. (2 marks)

Question 12. How does the mutual inductance of a pair of coils change when:

(i) the distance between the coils is increased?

(ii) the number of turns in each coil is decreased?

Justify your answer in each case. (2 marks)

Question 13. In a single slit diffraction experiment, if the width of the slit is doubled, how does the

(i) intensity of light and (ii) width of the central maximum change. Give reason for your answer. (2 marks)

Question 14. Draw the logic symbol of a 2-input NAND gate. Write down its truth table. (2 marks)

Question 15. A ray of light passes through an equilateral glass prism, such that the angle of incidence is equal to the angle of emergence. If the angle of emergence is 3/4 times the angle of the prism, calculate the refractive index of the glass prism. (2 marks

Question 16. A concave mirror and a convex lens are held separately in water. What changes, if any, do you expect in the focal length of either ? (2 marks)

Question 17. Derive an expression for the energy stored in a charged parallel plate capacitor with air as the medium between its plates. (2 marks)

Question 18. Draw the graph showing variation of thermo e.m.f. of a thermo-couple with the temperature difference of its junction. How does its neutral temperature vary with the temperature of the cold junction ? (2 marks)

Question 19. Derive an expression for the electric potential at a point along the axial line of an electric dipole. (3 marks)

Question 20. A copper voltameter is in series with a heater coil resistance 0.1 ohm. A steady current flows in the circuit for 20 minutes, and a mass of 0.99 gm of copper is deposited at the cathode. If the electro-chemical equivalent of copper is 0.00033 gm/coulomb, calculate the heat generated in the coil. (3 marks)

Question 21. State Huygen's postulates of wave theory. Sketch the wavefront emerging from a (i) point source of light and (ii) linear source of light like a slit. (1+2 marks)