CBSE Physics Previous Question Paper 
All India (Comptt.) 1998 (Part - 3)

Q. 1. Give the ratio of velocities of light rays of wavelengths 4000 A and 8000 A in vacuum.

Q. 2. A student obtains resistances of 3, 4, 12 and 16 ohms using only two metallic resistance wires either separately or joined together. What is the value of resistance of each of these wires?

Q. 3. Define ‘dielectric constant’ of a medium in terms of force between electric charges.

 

Q. 4. The wavelengths of some of the spectral lines obtained in hydrogen spectrum are 9546 A, 6463 k and 1216 A. Which one of these wavelengths belongs to Lyman series?

 

Q. 5. Write the truth table for the combination of gates shown here.

Q. 6. In a certain arrangement a proton does not get deflected while passing through a magnetic field region. Under what condition is it possible?

 

Q. 7. Give the phase difference between the applied a.c. voltage and the current in an LCR circuit, at resonance.

 

Q. 8. Refractive index of glass for lights of yellow, green and red colours are μy, μg and μr respectively. Rearrange these symbols in an increasing order of values.

 

Q. 9. Define ‘intensity of electric field’ at a point. At what points is the electric dipole field intensity parallel to the line joining the charges?

 

Q. 10. Capacitors P, Q and R have each a capacity C. A battery can charge the capacitor P to a potential V. If after charging P the battery is disconnected from it and the charged capacitor P is connected in following separate instances to Q and R
(i) to Q in parallel, and
(ii) to R in series ;
then what will be the potential differences between the plates of P in the two instances ?

 

Q. 11. Define ‘chemical equivalent’ and ‘electro-chemical equivalent’ of a substance. Establish the relationship between the two.

 

Q. 12. State and illustrate Curies law in magnetism.

 

Q. 13. How can the magnetic moments of two bar magnets of same size and mass be compared using a vibration magnetometer?

 

Q. 14. State Lenz’s law. Show that it is a consequence of the law of conservation of energy.

 

Q. 15. Prove mathematically that the average power over a complete cycle of alternating current through an ideal inductor is zero.

 

Q. 16. Draw a graph showing the variation of stopping potential with frequency of incident radiations in relation to photoelectric effect. Deduce an expression for the slope of this graph using Einstein’s photoelectric equation.

 

Q. 17. Define ‘disintegration constant* and ‘mean life’ of a radioactive substance. Give the unit for each.

 

Q. 18. Distinguish between n-type and p-type semi-conductors on the basis of energy-band diagram.

 

Q. 19. State Gauss’s theorem. Using Gauss theorem, derive an expression for electric field intensity at any point inside a hollow charged conducting sphere.

 

Q. 20. Why is a potentiometer preferred over a voltmeter to measure e.m.f. of a cell? The potentiometer wire AB shown in the figure is 400 cm long. Where should the free end of the galvanometer be connected on AB so that the galvanometer shows zero deflection?

 

Q. 21. A potential difference V is applied across a conductor of length L and diameter D. How are the electric field E and the resistance R of conductor affected when in turn
(i) V is halved,
(ii) L is halved and
(Hi) D is doubled?
Justify your  in each case.

Q. 22. When an alternating voltage of 220 V is applied across a device X, a current of 0.5 A flows through the circuit and is in phase with the applied voltage. When the same voltage is applied across another device Y, the same current again flows through the circuit but it leads the applied voltage by π/2 radians.
(a) Name the devices X and Y.
(b) Calculate the current flowing in the circuit when same voltage is applied across the series combination of X and Y.

 

Q. 23. Derive the expression for the fringe width in Young’s double slit interference experiment.

 

Q. 24. What is Doppler effect in light? The spectral line for a given element in light received from a distant star is shifted towards longer wavelength by 0.025%. Calculate the velocity of star in the line of sight.

 

Q. 25. Draw a labelled ray diagram for a refracting type astronomical telescope. How will its magnifying power be affected on increasing for its eye-piece (i) the focal length, and (ii) the aperture? Justify your .

 

Q. 26. Establish the relationship between the object distance, image distance and radius of curvature for a convex mirror.

 

Q. 27. Define ’solar constant’. Derive an expression for surface temperature of the sun in terms of solar constant and solar radius.

 

Q. 28. Explain with the help of a labelled diagram, the underlying principle, construction and working of a moving coil galvanometer.

 

Or

 

Explain with the help of a labelled diagram, the underlying principle, construction and working of a cyclotron.

 

 

Q. 29. State Bohr’s postulates. Using these postulates derive an ex¬pression for the total energy of an electron in the nth orbit of an atom. What does negative value of this energy signify?

 

Q. 30. Explain, with the help of a labelled circuit diagram the use of NPN transistor as an amplifier hi common emitter configuration. Why is a common emitter amplifier preferred over common base amplifier?