Question

Photoelectric effect was successfully explained by
(A) Hertz
(B) Planck
(C) Millikan
(D) Einstein

Answer 1

Hint The phenomenon of the photoelectric effect was first discovered in the year of 1839. But it was not until the year of 1905, that Einstein could successfully explain the law of the photoelectric effect.

Complete step by step answer
The photoelectric effect is the phenomenon where electrons are emitted from the surface of a metal when a light of a suitable frequency strikes on it.
According to the classical electromagnetic theory, there is a transfer in energy from the continuous lights waves to an electron. So on reducing the intensity of light, the kinetic energy of the electrons will be reduced. Thus when a metal is exposed to a dim light, then the electron should gather energy till it can leave the metal surface. But this hypothesis did not match with the experimental results.
It was seen that the electrons were emitted from the metal only when it was exposed to a light of a certain frequency or above. A low frequency beam could not build up enough energy for the electrons to leave the surface.
Albert Einstein successfully explained that the energy carried by the electromagnetic wave can only be released as packets of energy which are termed as photons. He theorised that the energy carried by each quantum of light was equal to the frequency of the light multiplied by a constant known as the Planck’s constant.
Therefore, it was Einstein who first successfully explained the photoelectric effect.
Hence the correct option is D.

Note
Millikan’s experimental observation supported the theory of Einstein’s photoelectric effect. Thus Einstein was awarded the Nobel Prize in Physics for the discovery of the law of photoelectric effect.