The constant A in the Richardson-Dushman equation for tungsten is 60 × 10^4 A/m^2-K. The work function of tungsten is 4.5 eV. A tungsten cathode having a surface area 2.0 × 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 × 10^-8 W/m^2-K4. Assume that the thermions take only a small fraction of the heat supplied.

Shane Macguire , 11 Years ago

Grade upto college level