**CBSE NOTES CLASS 12 PHYSICS **

**CHAPTER 11 DUAL NATURE OF RADIATION AND MATTER**

**Photon**

Photons are the packets of energy emitted by a source of radiation. The energy of each photon is,

E = hν,

where h is Planck’s constant and ν is frequency of radiation.

The rest mass of a photon is zero.

The momentum of a photon

$$\mathrm{p}\mathrm{}=\frac{\mathrm{h}\mathrm{\nu}}{\mathrm{c}}=\frac{\mathrm{h}}{\mathrm{\lambda}}$$

Dynamic or kinetic mass of photon,

$$\mathrm{}\mathrm{m}\mathrm{}=\frac{\mathrm{h}\mathrm{\nu}}{{\mathrm{c}}^{2}}=\frac{\mathrm{h}}{\mathrm{c}\mathrm{\lambda}}\mathrm{}$$

where c is speed of light in vacuum and λ is wavelength of radiation.

Photons are electrically neutral.

A body can radiate or absorb energy in whole number multiples of a quantum, that is hν, 2hν, 3hν …, nhν, where n is positive integer.