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Posted Date: 14 Jan 2009      Posted By:: Smt sangeeta mehta    Member Level: Silver    Points: 5 (Rs. 1)

2008 CBSE Gauss paper(Class:XII:Physics) Question paper



Course: Plus II   University/board: CBSE





Sample paper (Physics: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)
Question 22. Why is diffraction of sound waves easier to observe than diffraction of light waves? What two main changes in diffraction pattern of a single slit will you observe when the monochromatic source of light is replaced by a source of white light? (3 marks)

Question 23. Explain surface wave and sky wave propagations of radio waves. Why is short wave communication over long distances not possible by surface wave propagation? (3 marks)

Question 24. Give reasons for following observations on the surface of moon: (3 marks)

(i) Sun-rise and sun-set are abrupt

(ii) Sky appears dark

(iii) A rainbow is never observed.

Question 25. The energy levels of an atom of element are shown in the following diagram. Which one of the level transitions will result in the emission of photons of wavelength 620 nm? Support your answer with mathematical calculations. (3 marks)

Question 26. Give the logic symbol and truth table for AND gate. Explain, with the help of a circuit diagram, how this gate is realized in practices. (3 marks)

Question 27. Drawing a labeled circuit diagram, explain how a NPN transistor can be used as an amplifier in common base configuration. (3 marks)

Question 28. Explain the effect of introducing a dielectric slab between the plates of a parallel plate capacitor on its capacitance. Derive an expression for its capacitance with dielectric as the medium between the plates.

Or

Give the principle and explain the working of a Van de Graaff generator with the help of a labeled diagram (Marks 5)

Question 29. Explain the process of release of energy in a nuclear reactor. Draw a labeled diagram of a nuclear reactor and write the function of each part. (5 marks)

Question 30. Draw a labeled diagram of Thomson's experimental set-up to determine e/m of electrons. Explain by deriving the necessary mathematical expression how of electron can be determined by this method. (5 marks)





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