Physics: 2019: CBSE: [Delhi]: Set - III

In unpolarized light, the vibrations of light take place in all direction whereas in linearly polarized light, the vibrations of light take place in a direction perpendicular to the direction of wave motion.

For any given photosensitive material, there is a certain minimum cut off frequency at which photoelectric emission is possible. This minimum cut off frequency is called threshold frequency. Higher the work function of the material, greater is the threshold frequency.

Intensity is defined as the total amount of energy falling on a given surface per unit time per unit area.

 

When the temperature is increased, the electrons get excited, that is, a rise in temperature causes the atoms to vibrate more vigorously. This increases the number of collisions the electrons have, thereby decreasing the drift velocity.

The maximum frequency below which the signals can be transmitted from one point to another through the reflection from the ionosphere is 30 MHz. Above 30 MHz, the signals will be transmitted through the ionosphere and will not be reflected back.

The range of coverage in ground wave propagation depends on transmitted power and frequency.

The pattern of electric field lines when a point charge +q is kept near an uncharged conducting plate:

(a) (i) The threshold frequency is the lowest frequency of at which the emission of electrons from a specific metal surface takes place.

(ii) The stopping potential is defined as the minimum negative potential that is required to stop an electron from reaching the anode.

(b)
Graph of photocurrent versus anode potential for a radiation of frequency,  and intensities I₁ and I₂ (I₁ < I₂) is shown as:

 

Signal transmitted from a TV tower cannot be received beyond a certain distance because of the curvature of the earth.