The metal which has the highest work function among the following is:

The minimum value of electric field required to pull out electrons from a metal is approximately . . . . . . $V$/cm.

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

$(a)$ 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?

$A$ metallic surface with a work function of $2 \, eV$,on heating to a temperature of $800 \, K$,gives an emission current of $1 \, mA$. If another metallic surface having the same surface area,same emission constant,but a work function of $4 \, eV$ is heated to a temperature of $1600 \, K$,then the emission current will be......$mA$.

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