In an electron gun, electrons are accelerated by a potential difference $V$. If $e$ is the charge and $m$ is the mass of an electron, then the maximum velocity of these electrons will be

Assertion: In a photoemissive cell,an inert gas is used.
Reason: An inert gas in the photoemissive cell provides a greater current.

$(a)$ 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?

Positive rays were discovered by

Which of the following is not a property of cathode rays?

Atom or molecules can be visualized by which device or instrument?