Question

with regards to the Frank-Hertz experiment, How would increasing the temperature affect a graph of current vs accelerating voltage? Would there be a higher or lower background current? Sharper or less sharp peaks?

instinctually I want to say the increased temperature would lead to increased electron emissions and thereby current in the graph but im not sure what it would do to the peaks, im thinking it will make the slopes more gradual as there are more electrons and chances for them to make it through but I could also see that it would increase the chances of collisions and make the slopes sharper. either way could use some help.

Answer 1

When the tube temperature is increased it has nothing to do with the number of electron emission. Now, when the temperature of the tube increases, two things happen -

1. The peaks fall sharply.

Reason: The vapour pressure of mercury in the tube increases with the increase in temperature. Hence more collision takes place between the electrons and mercury atoms which reduces the mean free path of the electron. The peaks fall when the inelastic collision take place. If the number of collision increases, the energy transfer from electrons to the atoms will take place more readily. Hence, the peaks will fall sharply.

2. The background current increases.

Reason: During the elastic collision between electron and mercury atom, the kinetic energy of the electron also increases with the increase in temperature. Hence, when electrons reach the anode, the magnitude of current in the circuit also increases. This results in net increase of background current.