Question

What is photoelectric effect ? State the laws of photoelectric emission.

Answer 1

Photoelectric effect:
When the radiation such as $\gamma$-rays, $X$-rays, UV and even visible light fall on metals, electrons are emitted. This, phenomenon of emission of electrons is known as photoelectric effect.
Laws of Photoelectric Emission: The experimental observations on photoelectric effect may be summarized as follows, which are known as the fundamental laws of photoelectric emission.
i) For a given photo sensitive material, there is a minimum frequency called the threshold frequency, below which emission of photoelectrons stops completely, however great the intensity may be.
ii) For a given photosensitive material, the photo electric current is directly proportional to the intensity of the incident radiation, provided the frequency is greater than the threshold frequency.
iii) The photoelectric emission is an instantaneous process i.e., there is no time lag, between the incidence of radiation and the emission of photo electrons.
iv) The maximum kinetic energy of the photo electrons is directly proportional to the frequency of incident radiation, but is independent of its intensity.