Thermionic emission from a heated filament varies with its temperature $T$ as

In a Thomson set-up for the determination of $e/m$,electrons accelerated by $2.5 \ kV$ enter the region of crossed electric and magnetic fields of strengths $3.6 \times 10^4 \ Vm^{-1}$ and $1.2 \times 10^{-3} \ T$ respectively and go through undeflected. The measured value of $e/m$ of the electron is equal to

The number of secondary electrons emitted per number of primary electrons depends on:

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

In which of the following,emission of electrons does not take place?

In Thomson's method of determining $e/m$ of electrons,how are the electric and magnetic fields arranged relative to the electron beam?