Concept of Photon

Description:

In radiation-matter interaction, radiation i.e. light act as if made of particles called ‘photons’.

Photons are thought to be packets containing energy.

Photons also have frequency (v) and wavelength (λ)

Energy of photon is −

E = hv or hc/λ

Momentum is −

p = h/λ

Whatever is the intensity, all the photons of a given frequency (colour) have same energy individually (ℎ𝜈).

By increasing intensity, the number of photons increase but energy of each photon remains constant. As the number of photon increase, the number of electrons also increase and hence the current will increase.

All photons travel with the same speed, i.e. speed of light.

Frequency of photon give it a definite energy (colour), therefore when it enters a different medium, the colour (frequency) do not change.

In different medium its wavelength change and hence velocity change.

Rest mass of photon is zero hence its absorption does not change mass.