In which of the following,emission of electrons does not take place?

Which scientist invented cathode rays?

$(a)$ 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?

The filament of an electron gun is made of which material and coated with which material? Why?

The mass of the electron varies with

Three particles having their charges in the ratio of $1 : 3 : 5$ produce the same spot on the screen in Thomson's experiment. Their masses are in the ratio of