In $1897$,$J$.$J$. Thomson discovered which particle?

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

In Thomson's method of determining $e/m$ of electrons,how are the electric and magnetic fields arranged relative to the electron beam?

The thermionic emission of electrons is due to:

$A$ metallic surface with a work function of $2 \, eV$,on heating to a temperature of $800 \, K$,gives an emission current of $1 \, mA$. If another metallic surface having the same surface area,same emission constant,but a work function of $4 \, eV$ is heated to a temperature of $1600 \, K$,then the emission current will be......$mA$.

Which one is the correct relation for thermionic emission?