Cathode rays consist of

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

Which one of the following devices makes use of the electrons to strike certain substances to produce fluorescence?

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

An electron is:

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