Question

What is photoelectric effect? State the laws of photoelectric effect?

Answer 1

- Hint: Photo is a Greek word that means light, so it suggests the relation between electricity and light (photons).

Complete step-by-step solution -

Photoelectric effect is the phenomenon of emission of electrons from the surface of a metal when light photons (electromagnetic radiation) of a certain frequency strikes the metal surface.

Laws of photoelectric effect:
Emission of photoelectrons is an instantaneous process or we can say that there is no time delay in the photoemission process.
Number of photoelectrons emitted from the metal surface per second is directly proportional to intensity of incident light.
 A minimum frequency known as the Threshold frequency is required for the photoelectric effect to take place. The threshold frequency depends on the nature of the metal surface.
Velocity of emerging photo electrons from the metal surface depends only on the frequency of incident light and is independent of intensity of the light rays.
Additional information:
According to the wave theory, Energy of the electromagnetic waves is uniformly distributed across the wavefront and it depends only on the intensity of the incident light beam, which would mean that the kinetic energy of the electrons is directly proportional to intensity. But experimentally it was found that the kinetic energy is independent of the incident light intensity.
This discrepancy was resolved by Albert Einstein, he stated that light is made up of discrete packets of energy that are called Quanta. And each quantum has an energy given by:

The real life applications of this effect include – solar cells, photocells, photoconductive devices.

Note: During photoelectric emission from a surface of metal the photoelectrons can be emitted in any direction with any velocity between zero to the maximum velocity that can be acquired by the electron.