Physics Class XII

Question 1. Horizontal component of Earth's magnetic field at a place is 3 times the vertical component. What is the value of angle of dip at this place? (1 mark)

Question 2. Force between two point electric charges kept at a distance d apart in air is F. If these charges are kept at the same distance in water, how does the force between them change? (1 mark)

Question 3. Give any two factors on which thermo-electric emf produced in a thermo-couple depends. (1 mark)

Question 4. The electric current in a wire in the direction from B to A is decreasing. What is the direction of induced current in the metallic loop kept above the wire as shown in the figure? (1 mark)

Question 5. Name the electromagnetic radiations used for viewing objects through haze and fog. (1 mark)

Question 6. Give the ratio of the number of holes and the number of conduction electrons in an intrinsic semiconductor. (1 mark)

Question 7. In the given diagram, is the diode D forward or reversed biased? (1 mark)

Question 8. Name the planet which has maximum value of albedo. (1 mark)

Question 9. Two point electric charges of unknown magnitude and sign are placed a distance 'd' apart. The electric field intensity is zero at a point, not between the charges but on the line joining them. Write two essential conditions for this to happen. (2 marks)

Question 10. The variation of potential difference V with length l in case of two potentiometers X and Y is as shown in the given diagram. Which one of these two will you prefer for comparing emf's to two cells and why? (2 marks)

Question 11. Name any one material having a small value of temperature coefficient of resistance. Write one use of this material. (2 marks)

Question 12. Write two advantages and two disadvantages of a secondary cell over a primary cell. (2 marks)

Question 13. In the figure, the straight wire AB is fixed while the loop is free to move under the influence of the electric currents flowing in them. In which direction does the loop begin to move? Give reason for your answer. (2 marks)

Question 14. A radio frequency choke is air-cored coil whereas in audio frequency choke is iron-cored. Give reasons for this difference. (2 marks)

Question 15. An astronomical telescope consists of two thin lenses set 36 cm apart and has a magnifying power 8. Calculate the focal lengths of the lenses. (2 marks)

Question 16. Use the mirror formula to show that for an object lying between the pole and focus of a concave mirror, the image formed is always virtual in nature. (2 marks)

Question 17. An £-particle and a proton are accelerated through the same potential difference. Calculate the ratio of velocities acquired by the two particles. (2 marks)

Question 18. Describe the method used for determination of distance of a planet by parallax method. (2 marks)

Question 19. Explain the principle of a tangent galvanometer. How does the reduction factor of the galvanometer change, when (i) number of turns of the coil is increased and (ii) radius of the coil is decreased? Give reason for your answer in each case. (3 marks)

Question 20. A wire of uniform cross-section and length l has a resistance of 16 ohm. It is cut into four equal parts. Each part is stretched uniformly to length l and all the four stretched parts are connected in parallel. Calculate the total resistance of the combination so formed. Assume that stretching of wire does not cause any change in the density of its material. (3 marks)

Question 21. An electric heater and an electric bulb are rated 500 W, 220 V and 100 W, 220 V respectively. Both are connected in series to a 220 V a.c. mains. Calculate the power consumed by (i) the heater and (ii) electric bulb. (3 marks)