» CBSE PHYSICS Board Paper, 1998 Supplementary : CBSE Sample Question Papers

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

17. The thermo-emf of a thermo-couple is given by

θ is the temperature of the hot junction; a and p are the constants of the thermo-couple,
(i) Deduce an expression for the neutral temperature. 1
(ii) State two factors on which the temperature of inversion of a thermo-couple depends.1
Answer :

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. 2
Answer :

19. Calculate the equivalent resistance between the points A and B of the electric network given below. 3

Answer :

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. 3
Answer :

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 ?
(i) The widths of the two slits are increased equally.
{ii) The whole apparatus is kept in a denser medium. 3
Answer :

22. Sketch a graph showing the dependence of intensity of transmitted light on the angle of rotation between a polarizer and an analyser. A ray of light is incident at an angle of incidence i on the surface of separation between air and a medium of refractive index JI, such that the angle between the reflected and refracted rays is 90°. Obtain the relation between ip and µ. 3
Answer :

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. 3
Answer :

24. (i) 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. 3
Answer :

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. 3
Answer :

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 1 kilo-ohm. 3
Answer :

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. 3
Answer :

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. 5

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

29. (i) Write the working principle of a starter used along with a choke in a fluorescent tube.
2
(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. 3
Answer :

30. Draw a labelled diagram of Milhkan’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. 5
Answer :