Thermions are

Positive rays were discovered by

Write observations of various experiments which suggest that cathode rays are a stream of negatively charged particles.

What is the value (magnitude) of the electric field required for field emission?

Cathode rays are produced when the pressure is of the order of

The ratio of thermionic currents $(I/I_0)$ for a metal when the temperature is slowly increased from $T_0$ to $T$ is shown in the figure. ($I$ and $I_0$ are currents at $T$ and $T_0$ respectively). Which curve correctly represents this relationship?