Question

How does light exhibit traits of a particle?

Answer 1

All of us are aware of the fact that light has a dual nature: wave and particle nature. The evidence for the particle nature of light was the photoelectric effect, an experiment which wave theory of light failed to explain.

Complete answer:
Particle like traits of light are best explained by the phenomena photoelectric effect, the theory that was given by Albert Einstein.
“The photoelectric effect refers to the emission or ejection of electrons from the metal surface when an incident light of certain frequency falls on it.” Energy contained by this incident light is absorbed by the electrons in the metal which gives them enough energy to emit from the surface of the metal.
According to the classical wave approach, the energy of the electrons should increase with the intensity of the incident light which means the more the intensity of light, more will be the average energy carried out by an emitted electron.
However, experimentally it was observed that the energies of the emitted electrons were independent of the intensity of the light but these energies were proportional to another factor known as frequency of the incident light.
Einstein explained this by postulating that the electrons can receive energy from electromagnetic fields only in discrete units or bundles known as quanta or photons. When a photon of light having frequency higher than the threshold frequency strikes the metal surface, it transfers its energy to the electron which leads to its emission from the metal surface. Also, no amount of light with frequency below threshold frequency could help to eject the electrons.
An amount of energy E carried by a photon is mathematically explained as follows:-
$E=h\cdot \nu$
where,
h = Planck's constant ($6.626\text{ }\times \text{ }{{10}^{-34}}~Js$ )
ν = frequency of the incident photon
This phenomena of photoelectric effect explained that light consists of a stream of tiny particles and hence, we can say that light exhibits traits of particles.

Note:
The energy carried by the photon can also be expressed and used in terms of wavelength as follows:-
$E=h\cdot \nu =h\cdot \dfrac{c}{\lambda }\text{ (as v = }\dfrac{c}{\lambda }\text{)}$
where,
c = speed of light ($3\times {{10}^{8}}m/s$ )
$\lambda$ = wavelength of the incident photon.