CBSE Delhi-Set-3-2012

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

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  .

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.

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.

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,

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.

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:

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.

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

Mutual induction is the property by virtue of which, an emf is induced in one coil due to the current changing in the neighboring coil. 
The coefficient of mutual inductance of the two coils is numerically equal to the amount of magnetic flux  linked with the coil when a unit current (I) flows through the other coil and is given by,