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

The relation between current and charge is given by $I = A T^2 e^{qV / V_L}$. What is the value of $V_L$?

$A$ 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......$mA$.

Write observations of various experiments which suggest that cathode rays are a stream of negatively charged particles.

For a thermionic emitter (metallic),if $J$ represents the current density and $T$ is its absolute temperature,then the correct curve between $\log_e \frac{J}{T^2}$ and $\frac{1}{T}$ is:

Who discovered the presence of electric charge on an electron?