CBSE Board Sample Paper – 2010
Class – XII
Subject – Physics
General Instructions :
(i) All questions are compulsory.
(ii) Question numbers 1 to 8 are very short answer type questions, carrying one mark each.
(iii) Question numbers 9 to 18 are short answer type questions , carrying two marks each.
(iv) Question numbers 19 to 27 are also short answer type questions, carrying three marks each.
(v) Question numbers 28 to 30 are long answer type questions, carrying five marks each.
(vi) Use of calculators is not permitted. However, you may use log tables, if necessary.
1. In a hydrogen atom, an electron revolves around a proton. Which of these two exerts a greater electrostatic force on the other?
2. Draw an equipotential surface for a uniform electric field.
3. Define mobility. What is its S.I unit?
4. In the diagram , the radii of the trajectories of proton and alpha particles having equal momenta moving perpendicular to the uniform magnetic field are shown. Which one corresponds to alpha particle?
5. Can a body possess a charge 6.4 x 10 -20C? Explain.
6. An electric dipole of dipole moment 20 X 10-6 Cm is enclosed by a closed surface. What is the net flux coming out of the surface?
7. Two slits in young’s double slit experiment are illuminated by two different sodium lamps emitting light of same wavelength. No interference pattern will be obtained. Comment.
8. Name the phenomenon responsible for the reddish appearance of the sun at sunrise and sunset.
9. On the same graph plot the variation of E versus R and V versus R for a point charge.
10. Define electric field intensity. Write its S.I. unit. Write the magnitude and direction of electric field intensity due to an electric dipole of length 2a at the mid point of line joining the charges.
11. (a) Can two equi-potential surfaces intersect each other? Explain.
(b) Two charges – q and + q are located at points A (0, 0, -a) and B (0, 0, +a) respectively. How much work is done in moving a test charge 2 µC from point P (7, 0, 0) to Q (-3, 0, 0)?
12. Draw the block diagram, showing the various components of a generalized communication system and explain the role of a ‘repeater’ in such a system.
13. A charge q is placed at the center of the line joining to equal charges Q. Show that the system of three charges will be in equilibrium if q=-Q/4.
14. Keeping the voltage of the charging source constant, What would be the percentage change in the energy stored in a parallel plate capacitor , if the area of each plate is increased by 10%?
15. How does the frequency of a beam of ultraviolet light change when it goes from air into glass?
16. Explain briefly how an amplitude modulated wave is produced?
17. Two resistors are connected in parallel b/w A and B to give a net resistance of 2 ohms. When one of these resistors is broken, the net resistance becomes a 3 ohms. What is the resistance of the resistor that was broken?
18. Two wires X, Y have the same resistivity, but their cross-sectional areas are in the ratio 2 : 3 and lengths in the ratio 1 : 2. They are first connected in series and then in parallel to a d.c. source. Find out the ratio of the drift speeds of the electrons in the two wires for the two cases.
19. Show that the far field of a solenoid resembles that of a bar magnet. Hence define the magnetic moment of a solenoid.
20. A coil of number of turns N, area A, is rotated at a constant angular speed , in a uniform magnetic field B, and connected to a resistor R. Deduce expressions for :
(i) Maximum e.m.f. induced in the coil.
(ii) Power dissipation in the coil.
21. State Kirchoff’s rules of electrical networks. On the basis of this, obtain Wheatstone’s principle.
22. State Gauss’s law. Using this law , derive an expression for electric field due to a line of charge having linear charge density l.
23. (i) Show mathematically, an amplitude modulated signal contains the frequencies wc, wc+wm and wc - wm, where the symbols have their usual meanings.
(ii) Draw the block diagram to illustrate the process of amplitude modulation.
24. Draw a labeled ray diagram to show how an image is formed by compound microscope. On what factors will (i) its resolving power and (ii) its magnifying power depend?
25. The distance between two point sources of light is 24 cm. Find out where you will place a converging lens of focal length 9 cm, if the images of both are formed at the same point.
26. Draw the well labeled dig for the astronomical telescope, when the image formed at the least distance of distinct vision.
27. Distinguish between frequency modulation and amplitude modulation. Why is an FM signal less susceptible to noise than an AM Signal?
28. (a) Using a labeled diagram explain the construction and working of a moving coil galvanometer. Define its current and voltage sensitivity and explain how they can be increased.
(b) A galvanometer with a coil resistance of 5 ohm can tolerate a maximum current of 10mA. Explain how this can be converted into an ammeter of range 1A.
29. (a) With the help of a labeled ray diagram, show the image formation by a compound microscope. Derive an expression for its magnifying power.
(b) How does the resolving power of a compound microscope get affected on
(i) decreasing the diameter of its objective?
(ii) increasing the focal length of its objective?
30. A straight thick long wire of uniform cross section of radius ‘a’ is carrying a steady current I. Use Ampere’s circuital law to obtain a relation showing the variation of the magnetic field (Br) inside and outside the wire with distance r, (r £ a) and (r > a ) of the field point from the centre of its cross section. Plot a graph showing the nature of this variation. Calculate the ratio of magnetic field at a point a/2 above the surface of the wire to that at a point a/2 below its surface. What is the maximum value of the field of this wire?