Question

In a cathode ray tube, state:
(i) the purpose of covering cathode by thorium and carbon.

(ii) the purpose of the fluorescent screen.

(iii) how is it possible to increase the rate of emission of electrons.

Answer 1

(i) The purpose of covering cathode by thorium and carbon is to decrease the work function.

(ii) When electron beam on striking the screen gives a bright spot on it due to the fluorescence of the material coated on it.

(iii) On increasing the filament current, the rate of emission of electrons from the cathode will increase.