The color of the positive column in a gas discharge tube depends on:

Thermions are

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

How can the mass of an electron be obtained?

Cathode rays travelling from east to west enter into a region of an electric field directed towards north to south in the plane of the paper. The deflection of cathode rays is towards:

$(a)$ Estimate the speed with which electrons emitted from a heated emitter of an evacuated tube impinge on the collector maintained at a potential difference of $500\;V$ with respect to the emitter. Ignore the small initial speeds of the electrons. The specific charge of the electron,$i.e.$,the $e/m$ is given to be $1.76 \times 10^{11}\; C\; kg^{-1}$.
$(b)$ Use the same formula you employ in $(a)$ to obtain electron speed for a collector potential of $10\;MV$. Do you see what is wrong? In what way is the formula to be modified?