The constant `A` in the Richardson-Dushman equation for tungsten is `60 xx 10^(4)  A m^(-2)`. The
Channel: Doubtnut
Date: 2020-07-12

The constant `A` in the Richardson-Dushman equation for tungsten is `60 xx 10^(4)  A m^(-2)`. The work function of tungsten is `4.5 eV`. A tungsten cathode having a surface area `2.0 xx 10^(-5) m^2` is heated by a `24 W` electric heater. In steady state, the heat radiated by the cathode equals the energy input by the heater and the temperature becomes constant. Assuming that the cathode radiates like a blackbody, calculate the saturation current due to thermions. Take Stefan constant `= 6 xx 10^(-8) W m^(-2) K^(-4)`. Assume that the thermions take only a small fraction of the heat supplied.