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

In a discharge tube at $0.02\, mm$ pressure,there is a formation of
[$AIPMT$ $1996$]

$A$ metal plate gets heated when cathode rays strike against it due to:

In the phenomenon of electric discharge through gases at low pressure,the coloured glow in the tube appears as a result of
[$AIPMT$ $2008$]

For a thermionic emitter (metallic),if $J$ represents the current density and $T$ is its absolute temperature,then the correct curve between $\log_e \frac{J}{T^2}$ and $\frac{1}{T}$ is:

The thermionic emission of electrons is due to: