CBSE Physics Previous Question Paper 
All India (Comptt.) 1998 (Part - 4)

Q. 1. In a medium the force of attraction between two point electric charges, distance’d’ apart, is F. What distance apart should these be kept in the same medium so that the force between them becomes 3F?

 

Q. 2. Name the experiment which established the quantum nature of electric charges.

 

Q. 3. Draw energy-band diagram of a p-type extrinsic semiconductor.

Q. 4. An electron and proton moving with the same speed enter the same magnetic field region at right angles to the direction of the field. For which of the two particles will the radius of the circular path be smaller?

 

Q. 5. Two electric bulbs A and B are marked 220 V, 60 W and 220 V, 100 W respectively. Which one of the two has greater resistance?

 

Q. 6. An ideal inductor is in turn put across 220 V, 50 Hz and 220 V, 100 Hz supplies. Will the current flowing through it in the two cases be the same or different?

 

Q. 7. Write the following radiations in an ascending order in respect of their frequencies
X-rays, micro-waves, ultraviolet rays and radio waves.

 

Q. 8. Write the truth table for the following combination of gates

 

Q. 9. Two identical point charges of charge ‘£»’ are kept at a distance V* from each other. A third point charge is placed on the line joining the above two charges such that all the three charges are in equilibrium. Calculate the magnitude and location of the third charge.

 

Q. 10. When a capacitor is connected in series with a series L-R circuit, the alternating current flowing in the circuit increases. Explain why?

 

Q. 11. V-l graph for a metallic wire at two different temperatures T₁ and T₂ is as shown in the following figure. Which of the two temperatures T₁ and T₂ is higher and why?

Q. 12. Explain the principle on which the working of a potentiometer is based. Why is the use of a potentiometer preferred over that of a voltmeter for measurement of emf of a cell?

 

Q. 13. State the working principle of a tangent galvanometer. Write the mathematical expression for measuring currents using the tangent galvanometer.

 

Q. 14. You are given two identical looking bars A and B. One of these is a bar magnet and the other an ordinary piece of iron- Give an experiment to identify which one of the two is a bar magnet. You are not to use any additional materials for experiment.

 

Q. 15. Define the terms ‘luminous flux’ and ‘luminous intensity’. How are these two related to each other?

 

Q. 16. How does the (i) magnifying power and (ii) resolving power of a telescope change on increasing the diameter of its objective? Give reasons for your .

 

Q. 17. Explain laws of photoelectric emission on the basis of Einstein’s photoelectric equation.

 

Q. 18. Calculate the half life period of a radioactive substance if its activity drops to 1/16th of its initial value in 30 years.

 

Q. 19. A potential difference of 2 volt is applied between the points A and B shown in the network drawn in the figure. Calculate
(i) equivalent resistance of the network across the points A and B, and
(it) the magnitudes of currents flowing in the arms AFCEB and AFDEB.

 

Q. 20. The potential difference across the terminals of a battery of emf 12 V and internal resistance 2 Ω drops to 10 V when it is connected to a silver voltmeter. Calculate the silver deposited at the cathode in half an hour. Atomic weight of silver is 107.9 g mole?

 

Q. 21. Derive a formula for the force between two parallel straight conductors carrying current in opposite directions and write the nature of the force. Hence, define an ampere.

 

Q. 22. What are coherent sources of light? Why is no interference
Pattern observed when two coherent sources are
(1) infinitely close to each other ?
(ii) far apart from each other ?

 

Q. 23. A slit of width’d’ is illuminated by light of wavelength 6500 A. For what values of‘d’ will the
(i) first minimum fall at an angle of diffraction of 30°?
(ii) first maximum fall at an angle of diffraction of 30° ?

 

Q. 24. Draw a ray diagram to show the formation of the image of an object placed between f and 2f of a thin concave lens. Deduce the relation between the object distance, the image distance and the focal length of the lens under this condition.

 

Q. 25. Define the terms ‘potential barrier’ and depletion region’ for a p-n junction diode. State how the thickness of depletion region will change when the p-n junction diode is
(i) forward biased.

(ii) reverse biased ?

Q. 26. With the help of a labelled circuit diagram, explain the use of a transistor as an oscillator.

 

Q. 27. Define ‘absolute magnitude of a star. Assuming that the dimmest star visible to the naked eye has a magnitude of 6, compare its brightness with that of planet Venus which has a magnitude of - 4.

 

Q. 28. Derive an expression for the energy stored in a parallel plate capacitor with air as the medium between its plates. How does the total energy stored by the capacitor change when the medium of air is replaced by a medium of dielectric constant k? Explain.

 

Q. 29. By using Bohr’s postulates of atomic model derive mathemati¬cal expressions for (i) kinetic energy and (ii) potential energy, of an electron revolving in an orbit of radius r. How does the potential energy change with increase in the principal quantum number (n) for the electron and why?

 

Q. 30. (a) Draw the graphs showing the variation of reactance of (i) a capacitor, and (ii) an inductor with the frequency of an a.c circuit.
(b) 11 KW of electric power can be transmitted to a distant station at (0 220 V, or (ii) 22,000 V. Which of the two modes of transmission should be preferred and why? Support your  with possible calculations.

 

Or

 

Prove that an ideal inductor does not dissipate power in an a.c. circuit, A sinusoidal voltage V = 200 sin 3141 is applied to a resistor of 10 Ω resistance. Calculate
(i) rms value of the voltage, (ii) rms value of the current, and (iii) power dissipated as heat in watts.