Planck's quantum theory and photons

Planks quantum Theory:   

To explain the black body radiation Plank assumed that the energy of oscillatory particles should be discrete rather then continues.


According to him the oscillators can emit or absorb energy in the packets.

- Energy carried by each photon is hv.

- E=n h v where n= 1,2,3,.....

h is a planks constant.The value of

h=6.625 × 10^−34 J.s

Thus photons are particles of electromagnetic radiation emitted by source of radiation .

The important characteristics of photons are:

1. Energy of photons is E=hv = hc/λ,

where v is frequency of photons and c is velocity of radiation.
2.All photons travel with the same speed which is equal to speed of light i.e c =3 x 10^8 m/s.
3. The speed of photons is different in different media.
4. Photons of different wavelengths (λ)move with different speeds in the same medium.
5.The photons travels in straight lines.
6.Rest mass of photon is zero.
7. Momentum of a photon=Mass x velocity
=h/λ
8.Energy of a photon is usually expressed in electron volt (eV).
1eV=1.6 x 10^-19J
9.There is no charge on photons. Hence they are not deflected by electric and magnetic fields.