Write four laws of photoelectric effect.

Hint:Photoelectric effect is the phenomenon of emission of electrons from the surface of metals when light or any other radiation of suitable frequency falls on the metal. The emission of electrons depends on the frequency of light and the number of emitted electrons depends on the intensity of the light.

Complete answer:
Let us first understand what photoelectric effect is.Photoelectric effect is the phenomenon of emission of electrons from the surface of metals when light or any other radiation of suitable frequency falls on the metal. Light consists of massless particles called photons. These photons possess some energy that is directly proportional to the frequency of the light.

When light is incident on the surface of the metal, the photons collide with the free electrons near the surface and transfer their energy into the electrons. If the energy is greater than a particular value, the electrons are ejected out of the metal. These ejected electrons are called photoelectrons.

Let us discuss the laws of the photoelectric effect.
1) Emission of electrons does not occur for all values of frequency of light. There exists a minimum value of frequency that is needed for the emission of the photoelectrons.

2) The number of photoelectrons emitted is directly proportional to the intensity of the light incident for a given metal and frequency of the light. This frequency is called threshold frequency.

3) If the frequency of incident light is greater than the threshold frequency, then the kinetic energy of the photoelectrons depends on the frequency of the light and not on the intensity of the light.

4) Photoelectric effect is an instantaneous process. Meaning, it occurs in no time. The time needed for an incident photon to remove an electron is ${{10}^{-9}}$ seconds.

Note: A photon eject a single electron from the surface of the metal. The threshold frequency depends on the nature of metal. Therefore, the value of threshold frequency is different for different types of metal.