CBSE Physics Previous Question Paper 
All India (Comptt.) 1998 (Part - 7)

1. How does the luminosity of a star vary with its mass?

 

2. State two factors by which the range of transmission of signals by a T.V. tower can be increased.

 

 

3. The ratio of the horizontal component to the resultant magnetic field of earth at a given place is 1/√2. What is the angle of dip at that place?

 

 

4. Why is a dark region observed in a discharge tube at very low pressures?

 

5. What is the ratio of the nuclear densities of two nuclei having mass numbers in the ratio 1 4?

 

 

6. If the frequency of the a.c. source in a LCR series circuit is increased, how does the current in the circuit change?

 

 

7. What is the work done in moving a 2 microcoulomb point charge from corner A to corner B of a Square ABCD when a 10 µC charge exists at the center of the square?

 

8. Why is the terminal voltage across a battery more than its e.m.f. during re-charging?

 

 

9. An electric flux of -5 x 10³ Nm² C ^-1 passes through a spherical Gaussian surface of radius 20 cm due to the charge placed at its center.
(i) Calculate the charge enclosed by the Gaussian surface.
(ii) If the radius of the Gaussian surface is double, how much flux would pass through the surface?

 

 

10. The variation of resistance of a metallic conductor with temperature is given below-

(i) Calculate the temperature coefficient of resistance from the graph.
(ii) State why the resistance of the conductor increase with rise in temperature.

 

 

11. Three identical ceils, each of e.m.f. 2 V, are connected in parallel. This combination is connected to a 5 ohm resistor. If the terminal voltage across the cells in the closed circuit is 1.5 V, calculate the internal resistance of each cell.

 

 

12. Using Stefan’s Law, explain briefly how the surface temperature of a planet can be measured.

 

 

13. Define resolving power of a telescope. How does diffraction limit its resolving power?

 

 

14. Define the terms (i) luminous intensity and («) illuminance. Write the relation between them.

 

 

15. An irregular shaped wire PQRS (as shown in figure) placed in a uniform magnetic field perpendicular to the plane of the paper changes into a circular shape. State, with reason, the direction of the induced current in the loop

 

 

16. Using a logic circuit, explain briefly how a 2-input NAND gate can be converted into a NOT gate.

 

 

17. The thermo-emf of a thermo-couple is given by
E = αθ +1/2 βθ2
θ is the temperature of the hot junction ; α and β are the constants of the thermo-couple.
(0 Deduce an expression for the neutral temperature.
(ii) State two factors on which the temperature of inversion of a thermo-couple depends.

 

 

18. The current sensitivity of a moving coil galvanometer increases by 20% when its resistance is increased by a factor of two. Calculate by what factor the voltage sensitivity changes.

 

 

19. Calculate the equivalent resistance between the points A and B of the electric network given below.

 

20. An electron beam of velocity v, moving in the plane of paper enters a region of uniform magnetic field which is perpendicular to the plane of the paper, and travels in a circular path.
(i) Deduce an expression for the time-period of the electron. (ii) Does the kinetic energy of electron change during this time? Give reason.

 

 

21. State two conditions for obtaining sustained interference pattern. What is the effect on the interference pattern in Young’s double-slit experiment due to each of the following operations?
(a) The widths of the two slits are increased equally.
(b) The whole apparatus is kept in a denser medium.

 

22. Sketch a graph showing the dependence of intensity of transmitted light on the angle of rotation between a polarizer and an analyser. Aray of light is incident at an angle of incidence ip on the surface of separation between air and a medium of refractive index μ, such that the angle between the reflected and refracted rays is 90°. Obtain the relation between ip and μ.

 

 

23. Draw a labelled ray diagram to show the formation of image of an object in a compound microscope. Write the expression for its magnifying power.

 

 

24. CO Why is the energy variation of the electrons emitted during a beta decay continuous?
(ii) Explain, with an example, whether the neutron-proton ratio increases or decreases during beta decay.

 

 

25. What is a zener diode? Give its symbolic representation. With the help of a circuit diagram, explain how it can be used as a voltage stabilizer.

 

26. (i) Draw a circuit diagram of a p-n-p transistor as an amplifier in a common emitter configuration.
(ii) Calculate the voltage gain for a transistor having a current gain 40, collector resistance 6 kilo-ohm and input resistance 1 kilo-ohm.

 

 

27. State the underlying principle of a tangent galvanometer. Write briefly how it can be used to determine the horizontal component of earth’s magnetic field at a given place.

 

 

28. Derive the expression for the energy stored in a charged capacitor. Show that there is always a loss of energy on connecting the two charged capacitors having capacitance C₁, C₂ and potentials V₁ V₂.

 

 

Or

 

 

Explain the construction and working of a Van de Graff generator with the help of a labelled diagram. Mention its use.

 

 

29. (i) Write the working principle of a starter used along with a choke in a fluorescent tube.
(ii) An inductance coil has a resistance of 100 ohm. When a.c. signal of frequency 1000 Hz is applied to the coil, the applied voltage leads the current by 45°. Calculate the self-inductance of the coil.

 

 

30. Draw a labelled diagram of Millikan’s oil drop experiment to determine the charge of an electron. Give its working principle.
Derive the expression for the charge in terms of the various parameters involved in the experiment. Mention the other fundamental information, besides the determination of the charge, drawn from this experiment.