CBSE Physics Previous Question Paper 
All India (Comptt.) 1998 (Part - 6)

Q. 1. Sketch the electric lines of force for two positive charges Q₁ and Q₂ (Q₁ > Q₂) separated by a distance d.

Q. 2. Why is a voltmeter always connected in parallel with a circuit element across which voltage is to be measured?

 

Q. 3. What is ‘ ‘Seebeck coefficient’?

Q. 4. Mention two properties of the alloy from which permanent magnets are made.

 

Q. 5. Give the direction in which the induced current flows in the wire loop, when the magnet moves towards it as shown in the figure.

 

Q. 6. Why do long distance radio broadcast use short wave bands?

 

Q. 7. At what angle of incidence should a light beam strike a glass slab of refractive index V3, such that the reflected and the refracted rays perpendicular to each other?

 

Q. 8. Name a planet which shows phases like the moon.

 

Q. 9. Two point charges + 4 μC and - 6 μC are separated by a distance of 20 cm in air. At what point on the line joining the two charges is the electric potential zero?

 

Q. 10. State Faraday’s first law of electrolysis. How is it used?

 

Q. 11. An electron of kinetic energy 25 keV moves perpendicular to the direction of a uniform magnetic Held of 0.2 millitesla. Calculate the time period of rotation of the electron in the magnetic field.

 

Q. 12. Define the coefficient of self-inductance. Write its unit. Give two factors on which the self-inductance of a long solenoid depends.

 

Q. 13. Briefly describe the work of Maxwell and Hertz in the field of electromagnetic waves.

 

Q. 14. A glass prism of refracting angle 60° and refractive index 1.5 is completely immersed in water of refractive index 1.33. Calculate the angle of minimum deviation of the prism in this situation. (sin-1 0.56 = 34.3°)

 

Q. 15. Draw a labelled ray diagram showing the formation of image of a distant object in an astronomical telescope.

 

Q. 16. Obtain the expression for the maximum kinetic energy of the electrons emitted from a metal surface in terms of the frequency of the incident radiation and the threshold frequency.

 

Q. 17. Pure silicon at 300 K has equal electron and hole concentra¬tions of 1.5 x 10¹⁶/m³. Doping by indium increases the hole concentration to 4.5 x 10²²/m³. Calculate the new electron concentration in the doped silicon.

 

Q. 18. With the help of a diagram, describe the method of determining the diameter of a planet.

 

Q. 19. ‘n’ identical cells each of emf ‘E’ and internal resistance ‘r’ are connected in series to a resistor ‘R’.
(i) Deduce an expression for the internal resistance ‘r’ of one cell in terms of the current ‘I’ flowing through the circuit.
(ii) How does the internal resistance of the cell vary with temperature?

 

Q. 20. Calculate the current drawn from the battery in the given network sketched here.

 

Q. 21. Derive the expression for the force between two infinitely long parallel straight wires carrying current in the same direction. Hence define one ampere.

 

Q. 22. A magnet oscillating in a horizontal plane, has a time period of 3 seconds at a place where the angle of dip is 30° and 4 seconds at another place, where the dip is 60°. Compare the resultant magnetic field at the two places.

 

Q. 23. Verify Snell’s law of refraction using Huygen’s wave theory.

 

Q. 24. A double convex lens made of glass of refractive index 1.5 has both radii of curvature of magnitude 20 cm. An object 2 cm high is placed at 10 cm from the lens. Find the position, nature and size of the image.

 

Q. 25. State two properties of nuclear forces. Prove that the density of matter in nuclei is independent of mass number A.

 

Q. 26. The output of a 2-input AND gate is fed to a NOT gate. Draw the logic circuit of the combination of gates. Give its logic symbol and write down its truth table.

 

Q. 27. Draw a circuit diagram of a common-emitter amplifier using a n-p-n transistor. Prove that in this amplifier, the output voltage is 180° out of phase with the input voltage.

 

Q. 28. An electric dipole is held in a uniform electric field. (i) Show that no translatory force acts on it. (ii) Derive an expression for the torque acting on it.
(iii) The dipole is aligned parallel to the field. Calculate the work done in rotating it through 180°.

 

Or

 

(i) Derive an expression for the energy stored in a parallel plate capacitor with air as the medium between its plates.
(ii) Air is replaced by a dielectric medium of dielectric constant ‘k’. How does it change the total energy of the capacitor?

 

Q. 29. (a) Draw the variation of the following with the frequency of the a.c. source
((i) reactance of an inductor, and
(ii) reactance of a capacitor.
(b) An a.c. circuit having an inductor and a resistor in series draws a power of 560 W from an a.c. source marked 210 V, 60 Hz. If the power factor of the circuit is 0.8, calculate ‘
(i) the impedance of the circuit, and
(ii) the inductance of the inductor used.

 

Q. 30. Draw a labelled diagram of Thomson’s set-up to find e/m of electrons. Briefly explain how the velocity of the electrons is determined? Assume that the p.d. between the cathode and the anode is the same as that between the two deflecting plates. If this p.d. is doubled, calculate by what factor the magnetic field should be changed to keep the electron beam still undeflected.