CBSE Physics Previous Question Paper 
All India (Comptt.) 1998 (Part - 10)

Q. 1. An electron and a proton are free to move in a given electric field. Will the acceleration experienced by them be equal or different?

Q. 2. Is the potential difference across the two p.n. junctions in the given circuit same or different?

Q. 3. The current-voltage graphs for a given metallic conductor at two different temperatures T₁ and T₂ are as shown in the diagram. Which of these two temperatures is higher?

Q. 4. A charged particle enters a uniform magnetic field at right angles. Of these three
(i) its kinetic energy,
(ii) its speed and
(iii) its linear momentum, which will change on entering the field region ?

Q. 5. Write the truth table for the NOT gate.

Q. 6. Give an example of interference of light from daily life situations.

Q. 7. Two thin lenses, of powers, 10D and - 5D are put together. What is the focal length of the combination?

Q. 8. Work functions for two metals A and B are 2 eV and 5 eV respectively. Which one of the two has higher threshold wavelength?

Q. 9. A charge q is placed at the centre of the line joining two equal charges Q and Q. Calculate the value of charge q such that all the three charges are in equilibrium. Also mention the nature of this charge.

Q. 10. State Faraday’s laws of electrolysis.

Q. 11. Of the two identical galvanometers, one is to be converted into an ammeter and the other into a milliammeter. Which of the two shunts will be of larger resistance and why?

Q. 12. Define ‘angle of dip’. What is the value of angle of dip at a place where horizontal and vertical components of earth’s magnetic field are equal?

Q. 13. Explain how a current carrying metallic loop acts as a magnetic dipole. How is the magnetic dipole moment affected on increasing the value of the current flowing through the loop?

Q. 14. Define ‘angular dispersion’ and ‘dispersive power’ for a prism. Write two factors on which the angular dispersion produced by a prism depends.

Q. 15. Calculate the distance at which an object should be placed in front of a thin convex lens of focal length 10 cm to obtain a virtual image of double its size.

Q. 16. You are given three lenses having powers P and apertures A as under
P₁ = 5D ; A₁ = 2 cm
P₂ = 2D ; A₂ = 10 cm
P₃ = 10D ; A₃ = 1 cm
Which of the two lenses will you select to construct a telescope and why?

Q. 17. Binding energy per nucleon for deutron (₁H²) and helium (₂He⁴) are 1.1 MeV and 7.0 MeV respectively. Calculate the energy released when two deutrons fuse together to form a helium nucleus.

Q. 18. Using Bohr’s postulate, derive an expression for the radius of the nth orbit of the electron in hydrogen atom.

Q. 19. For measuring e.m.f’s of cells, a potentiometer is preferred over a voltmeter. Why? The length of a potentiometer wire is 5 metres. It is connected to a battery of constant emf. For a given Leclanche cell, the position of zero galvanometer deflection is obtained at 100 cm. If the length of potentiometer wire be made S metres instead of 5 metres, calculate the length of wire for zero deflection in galvanometer for the same Leclanche cell.

Q. 20. By applying Kirchh off s laws, calculate the current flowing through each resistance in the network shown in this diagram.

Q. 21. Explain why two straight parallel metallic wires carrying electric current in the same direction, attract each other. Derive an expres¬sion for the force experienced in this situation.

Q. 22. An air core coil and an electric bulb are connected in series across a 220 V, 50 Hz a.c. source. The bulb glows with some brightness. How will the glow of the bulb be affected when
(i) an iron rod is introduced into the coil and .
(ii) a capacitor is introduced in series in the circuit ? Justify your  in each case.

Q. 23. Distinguish between ground wave propagation and sky wave propagation of radio waves. Why can sky wave propagation be not used for long distance T.V. transmission?

Q. 24. Describe an experiment to demonstrate transverse wave nature of light.

Q. 25. A transistor is used in common-emitter mode in an amplifier circuit. When a signal of 20 mV is added to the base-emitter voltage, the base current changes by 20 μ A and the collector current changes by 2mA. The load resistance is 5 x 10³ Ω. Calculate (0 current gain, and (ii) voltage gain of the transistor.

Q. 26. Define ’solar constant’ and ’solar luminosity’. Explain how their knowledge helps us to determine the surface temperature of the Derive the formula used.

Q. 27. Distinguish between a conductor, an insulator and a semicon¬ductor on the basis of energy-band diagram.

Q. 28. With the help of a labelled diagram, explain the principle, construction and working of a transformer. Why is the core of a transformer laminated?

Or

With the help of a labelled diagram, explain the principle, construction and working of an a.c. generator.

Q. 29. Define capacitance of a capacitor. Give its unit Derive an expression for the total capacitance when three capacitors of capacitances C1 C2 and C3 are connected in series. Write any two uses of capacitors in electrical circuits.

Q. 30. With the help of a labelled diagram, explain the principle and the method of determination of e/m of an electron by Thomson’s method. Derive the necessary formula