Explain: Photoelectric effect.

(N/A) Einstein $(1905)$ explained the photoelectric effect using Planck's quantum theory of electromagnetic radiation.
Shining a beam of light on a metal surface can be viewed as shooting a beam of particles called photons. When a photon of sufficient energy strikes an electron in the metal atom,it transfers its energy instantaneously to the electron,causing it to be ejected without any time lag.
The kinetic energy of the ejected electron is proportional to the frequency of the incident radiation and does not depend on the intensity of light.
Striking photon energy $= h\nu$
The minimum energy required to eject an electron is called the work function $(W = h\nu_{0})$.
According to the conservation of energy principle,the kinetic energy of the ejected photoelectron is given by:
$h\nu = W + \frac{1}{2} m_{e} V^{2}$
Substituting $W = h\nu_{0}$:
$h\nu = h\nu_{0} + \frac{1}{2} m_{e} V^{2}$
$\frac{1}{2} m_{e} V^{2} = h(\nu - \nu_{0})$
where $m_{e}$ is the mass of the electron,$V$ is the velocity of the ejected electron,and $\nu > \nu_{0}$. $A$ more intense beam of light contains a larger number of photons,resulting in a greater number of ejected electrons.