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LENIN said:I have a few questinons abut the cathodes in the tube.
If I understand them corectly they eject elecrons becouse of heat. But in vacuum tube thereis no air and the only way heat can be trensferd from the outside of the tube on to the cathodes is by infrared light. So it seams that they act a bit like the photoefect. So if I understan it the cathodes should slovley wear out and that would explein where the missing enthropy is.
Pleas corect me if I'm wrong.
I'll answer this for a generic cathode and not specificially for this particular experiment.
A thermionic cathode emit electrons via heating the cathode. You heat the cathode by passing current through it. So the fact that it is in vacuum is of no concern. In fact, in all of these cathodes, you want them to be in a vacuum or else electron transport is hindered.
A photocathode works using the photoelectric effect phenomena. There's no heating here. All you need are photons with energy larger than the cathode work function.
The cathodes in both setup do not exactly "wear out", because they are connected to ground i.e. they are typically grounded or connected in a closed circuit, so the electrons that left the surface are continually replenished. In a photocathode, especially, you definitely want it grounded because if you don't, you will have a build up of charges (charging effect) that will significantly alter the work function of the cathode.
Zz.
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