Write information about the negative electric charge emitted from metals when $UV$ light is incident on them or when metals are heated.

(N/A) In $1887$,it was observed that when ultraviolet $(UV)$ light is incident on a metal surface or when some metals are heated,negative charges are emitted from them.
Particles produced by these different methods exhibit similar characteristics. In $1897$,$J.J. Thomson$ identified these particles as electrons and demonstrated that the electron is a fundamental and universal constituent of matter. For the discovery of the electron,$J.J. Thomson$ was awarded the Nobel Prize in Physics in $1906$.
In $1913$,the American scientist $R.A. Millikan$ measured the charge of an electron using his oil drop experiment. He observed that the charge on any oil drop is always an integral multiple of the fundamental charge $e = 1.602 \times 10^{-19} \ C$. Thus,$Millikan$ proved that electric charge is quantized.
By knowing the specific charge $\frac{e}{m}$ and the elementary charge $e$,the mass of the electron $(m)$ can be calculated.