CBSE Physics
Sample Paper 1998
(Delhi) Part - 3
Set - 1
1. How does the luminosity of a star vary with its mass ? 1
2. State two factors by which the range of transmission of signals by a T.V. tower can be increased. 1
3.The ratio of the horizontal component to the resultant magnetic field of earth at a given place is 1/√2 . What is the angle of dip at that place ? 1
4. Why is a dark region observed in a discharge tube at very low pressures ? 1
5. What is the ratio of the nuclear densities of two nuclei having mass numbers in the ratio 14?
6. If the frequency of the a.c. source in a LCR series circuit is increased, how does the current in the circuit change ? 1
7. What is the work done in moving a 2 microcoulomb point charge from corner A to corner B of a square ABCD when a 10 µC charge exists at the centre of the square ? 1
8. Why is the terminal voltage across a battery more than its e.m.f. during re-charging ? 1
9. An electric flux of -5 x 103 Nm2
C -1 passes through a spherical Gaussian surface of radius 20 cm
due to the charge placed at its centre.
(i) Calculate the charge enclosed by the Gaussian surface. 1
(ii) If the radius of the Gaussian surface is doubled, how much flux would
pass through the surface ? 1
10. The variation of resistance of a metallic conductor
with temperature is given below.
(i) Calculate the temperature coefficient of resistance from the graph. 1
(ii) State why the resistance of the conductor increases with rise in
temperature. 1
11. Three identical cells, each of e.m.f. 2 V, are
connected in parallel. This combination is connected to a 5 ohm resistor. If
the terminal voltage across the cells in the closed circuit is 1.5 V,
calculate the internal resistance of each cell. 2
12. Using Stefan’s Law, explain briefly how the
surface temperature of a planet can be measured. 2
13. Define resolving power of a telescope. How does
diffraction limit its resolving power ? 2
14. Define the terms (i) luminous intensity and (ii)
illuminance. Write the relation between them.
15. An irregular shaped wire PQRS (as shown in figure) placed in a uniform magnetic field perpendicular to the plane of the paper changes into a circular shape. State, with reason, the direction of the induced current in the loop.
Set - 2
Q. 1. Name the physical quantity whose S.I. unit is coulomb/volt.
Q. 2. Write the frequency limit of visible range of electromagnetic spectrum in k Hz.
Q. 3. How does the conductance of semiconducting
material change with the rise in Temperature ?
Q. 4. The force F experienced by a particle of charge e moving with velocity v in a magnetic field B is given by
Of these, name the pairs of vectors which are always at right angles to
each other. 1
Q. 5. Two wires A and B are of same metal, have the same
area of cross-section and have their lengths in the ratio 2 1. What
will be the ratio of currents flowing through them respectively the same
potential difference is applied across length of each of them ?
Q. 6. Calculate the rms value of alternating current
shown in the figure.
Q. 7. The image of an object formed on the screen is not in sharp focus. Suggest a method to get clear focussing of the image on the screen without disturbing the position of the object, the lens or the screen.
Q. 8. Two protons A and B are placed between two
parallel plates have potential difference V as shown in figure. Will the
proton experience equal or unequal force ?
Q. 9, Define the terms threshold frequency and stopping
potential for photoelectric effect. Show graphically how the stopping
potential for a given metal varies with frequency of the incident radiation,
Mark threshold frequency on the graph.
Q. 10. Draw a labelled diagram of Laclenche cell. Write
down the function of charcoal powder and manganese dioxide used in porous
pot.
Q. 11. How does the mutual inductance of a pair of coils
changes when (i) Distance between the coil is increased ? (ii) the number of
turns in each coil is decreased ? 2
Justify your in each case.
Q. 12. Define the terms magnetic inclination and
horizontal component of earth’s magnetic field at a place. Establish the
relationship between the two with the help of a diagram.
Q. 13. An electron in an atom revolves around the
nucleus in an orbit of radius 0.53 A. Calculate the equivalent magnetic
moment if the frequency of revolution of electron is 68 X 10 MHz.
Q. 14. Write the function of base region of a
transistor. Why is this region made thin and slightly doped ?
Q. 15. Derive an expression for the energy stored in a parallel plate capacitor with air as the medium between the plates.