Particle Nature of light: Einstein's Explanation.

 Particle Nature of light: Einstein's Explanation.

Einstein extended Planck's quantum concept to explain the photoelectric effect in 1905. According to Einstein, the energy in light is not spread out over wavefronts but is concentrated in small packets or energy quanta. Therefore, light (or any other electromagnetic waves) of frequency v from any source can be considered as a stream of quanta and the energy of each light quantum is given by E=hv.

[1] 

He also proposed that a quantum of light has linear momentum and the magnitude of that linear momentum is p=h/c. The individual light quantum of definite energy and momentum can be associated with a particle. can behave as a particle and this is called photon. Therefore, photon is nothing but particle manifestation of light.

Light is made up of particles called Photons.

Characteristics of photons:

According to particle nature of light, photons are the basic constituents of any radiation and possess the following characteristic properties:

i) The photons of light of frequency v and wavelength & will have energy, given by E=hv= hc/λ

ii) The energy of a photon is determined by the frequency of the radiation and not by its intensity and the intensity has no relation with the energy of the individual photons in the beam.

iii) The photons travel with the speed of light and its momentum is given by hhv P=h/λ =hv/c

iv) Since photons are electrically neutral, they are unaffected by electric and magnetic fields.

v) When a photon interacts with matter (photon-electron collision), the total energy, total linear momentum and angular momentum are conserved. Since photon may be absorbed or a new photon may be produced in such interactions, the number of photons may not be conserved. 

“Matter is Energy… Energy is Light…We are all Light Beings” —Albert Einstein.