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

The order of the $q/m$ ratio for a proton,$\alpha$-particle,and electron is:

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

$A$ cathode emits $1.8 \times 10^{14}$ electrons per second when heated. When $400 \ V$ is applied to the anode,all the emitted electrons reach the anode. The charge on an electron is $1.6 \times 10^{-19} \ C$. The maximum anode current is ............ $\mu A$.

An oxide-coated filament is useful in vacuum tubes because essentially:

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?