According to the study of photoelectric effect, if light interacts with matter it behaves the packets of energy. These packets of energy are called as quanta’s or photons. Scientist Einstein gave the important conclusions about the wave particle theory of light.
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Postulates of Wave Particle Theory of LightThe characteristics of the wave particle theory are given below:(i)The energy of each photon is h`nu` , where h is called the Plank’s constant and `nu` is the frequency of light wave.(ii) In interaction of radiation with matter, radiation behaves as if it is made of particles like photons.(iii) Each photon has energy E = h`nu` = hc/`lambda` and momentum p = h`nu`/c = h/`lambda`, where h is Plank’s constant, `nu` is the frequency of light, l is the wavelength of light and c is the velocity of light.(iv)
Irrespective of the intensity of radiation, all the photons of a particular frequency `nu` or wavelength l have the same energy E = h`nu` = hc/`lambda` and the same momentum p = h`nu`/c = h/`lambda`.(v) By increasing the intensity of radiation of a given frequency or wavelength on a metal surface, there is only increase in the number of photons per second falling on that surface, while each photon is having the same energy.
It shows that the photon energy is independent of intensity of light.Wave Particle Theory of Light : more Postulates(vi) All the photons emitted from the source of radiations travel through the space with the same speed that is the speed of light in space.(vii) The frequency of the photon gives the radiation, a definite energy or colour which does not change when photon travels through different medium.
(viii) The velocity of photon in different mediums is different which is due to the change in wavelength.(ix) The photon mass is zero.(x) Photons are not deflected by the electric and magnetic fields, which shows that photons are neutral in nature.(xi) In a photon particle collision, the energy and the momentum are conserved. But the number of photons may not be conserved in the collision.
Wave Particle Theory of Light : ConclusionThe famous scientist Einstein made an important conclusion that the light quantum can be associated with momentum p = hu/c = h/l, where c is the velocity of light in vacuum. A definite value of energy as well as momentum gives the strong indication that the light quantum is a particle, which is called as photon.