# CBSE Delhi-Set-1-2012

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• 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

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:

• Q7

Why should electrostatic force be zero inside a conductor?

Marks:1

An electric conductor has a large number of free electrons. When the conductor is placed in an electric field, these electrons redistribute themselves on the surface of the conductor to make the field zero inside the conductor.

• Q8

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

Marks:1

According to the Lenz’s Law, the current will be induced in a direction that opposes the increase of magnetic flux. The current I gives rise to a magnetic field in the outward direction through ring 1 & inward direction through ring 2.
Since the current (I) is steadily increasing in the wire, 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

The susceptibility of a magnetic material is  . Identify the type of magnetic material and state its two properties.

Marks:2

Since the susceptibility of the given material is negative, it is a diamagnetic material.
The properties of diamagnetic materials are as follows:
(i) A diamagnetic material placed inside a magnetic field gets feebly magnetized in a direction opposite to the direction of the magnetizing field.
(ii) Diamagnetic materials do not obey Curie’s law and their magnetic behavior does not change with a change in the temperature.