# CBSE Delhi-Set-3-2012

To Access the full content, Please Purchase

• Q1

The horizontal component of the earth's magnetic field at a place is B and angle of dip is 60°. What is the value of vertical component of earth's magnetic field at equator?

Marks:1

On the equator,  and therefore the vertical component of earth's magnetic field is also zero.

• Q2

Name of physical quantity which remains same for microwaves of wavelength 1 mm and UV radiations of 1600 Å in vacuum.

Marks:1

Microwaves and UV radiations are a part of the electromagnetic spectrum. The physical quantity that remains same for both the radiations is their speed of propagation in vacuum, which is equal to  .

• Q3

Under what conditions does a biconvex lens of glass having a certain refractive index act as a plane glass sheet when immersed in a liquid?

Marks:1

A biconvex lens will act as a plane sheet of glass if it is immersed in a liquid that has the same refractive index as the material of the biconvex lens. In this case, the focal length of the lens becomes infinite.

• Q4

When electrons drift in a metal from lower to higher potential, does it mean that all the free electrons of the metal are moving in the same direction?

Marks:1

When an electric field is applied across a conductor, the electrons drift from lower to higher potential. The drift velocity of the electrons gets superimposed on the thermal velocity and as a result, each electron moves in the direction of the resultant of the drift and the thermal velocity. Thus, the resultant velocity and hence the direction of motion may be different for different electrons. The electrons may also collide with ions and may change its direction of motion.

• Q5

State de Broglie hypothesis.

Marks:1

According to the de Broglie hypothesis, a moving material particle (whether big or small) having a momentum ‘p’ will always have a wavelength  associated with it. Such waves are called matter waves or de Broglie waves having a wavelength,

• Q6

Why is electrostatic potential constant throughout the volume of the conductor and has the same value (as inside) on its surface?

Marks:1

The electric potential is defined as the work done in taking a unit positive charge from infinity to that point. The electric field inside a conductor is zero, i.e. E = 0.
Hence no additional work is done in taking a charge from the surface to anywhere inside the conductor and the electrostatic potential remains constant throughout the volume of the conductor and has the same value as that on the surface.

• Q7

Show on a graph, the variation of resistivity with temperature for a typical semiconductor.

Marks:1

As the temperature of a semi conductor is increased, the number density of electrons and that of holes increases. Therefore, its resistivity decreases with increasing temperature. The following curve shows the variation of resistivity with temperature for a typical semiconductor:

• Q8

Predict the direction of induced current in metal rings 1 and 2 when current I in the wire is steadily decreasing?

Marks:1

According to the Lenz’s Law, the current will be induced in a direction that opposes the change in magnetic flux. Since the current (I) is steadily decreasing in the wire, it will give rise to a decreasing magnetic field in the inward direction. The current will be induced in the direction such that the induced current opposes the decrease or reinforces the magnetic field in the inward direction. According to the Maxwell’s right hand rule, the induced current will be in the clockwise direction in ring 1 and in the anticlockwise direction in ring 2.

The red arrows show the direction of induced current in the rings.

• Q9

Draw a plot showing the variation of (i) electric field (E) and (ii) electric potential (V) with distance r due to a point charge Q.

Marks:2

Therefore, the electric field  shows an inverse square relationship whereas, the electric potential ‘V’ shows an inverse relationship with distancer’ as shown below:

• Q10

Define mutual inductance between two long coaxial solenoids. Find out the expression for the mutual inductance of inner solenoid of length l having the radius r1 and the number of turns n1 per unit length due to the second outer solenoid of same length and n2 number of turns per unit length.

Marks:2