Are the anodes and cathodes in a vacuum tube truly charged? Can I treat them like any other charged object? also how can I calculate the charge? How would I calculate the alternating charge if it's ac?
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1Start with thermionic emission (pdf) and then add in how vacuum tubes really work for extra credit. – jonk May 11 '18 at 00:16
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2You should explain why you are asking these questions. They don't make a lot of sense in the context of designing circuits with tubes. – Olin Lathrop May 11 '18 at 11:44
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Are the anodes and cathodes in a vacuum tube truly charged?
They are if you apply a voltage between them.
Can I treat them like any other charged object?
That depends on what the point is, but in the general case, no. That's because there is a lot more going on in a vacuum tube than just the capacitance between the anode and cathode.
how can I calculate the charge?
The datasheet should give you some idea of the anode/cathode capacitance, or you could measure it. From that you can find the charge as a function of applied voltage like you would with any capacitor.
However, this isn't a very useful parameter when designing circuits with tubes.
How would I calculate the alternating charge if it's ac?
This question seems to indicate you don't understand how tubes work in the first place. Tubes only conduct in one direction, so AC isn't relevant, depending on what exactly you mean by that.
In general, what you are asking aren't the kinds of questions one normally asks when designing circuits with tubes. You should pop up a few levels and explain what you are trying to accomplish, and why you want to use tubes to accomplish it. Some of them new-fangled transistorators might be just what you need.
Olin Lathrop
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Yes and no. In normal use there's anode voltage between anode and cathode. Being metallic parts the interiors of the tube can be seen as capacitors. So there's surely some +charge in anode and some -charge in cathode. The voltages of the other electrodes affect, too, because more complex tubes can be seen as a capacitor network.
Capacitance is not enough to explain the working of the tube. The electron emission and the resulted charge cloud make all pretty complex. The charge flowing through the vacum makes the tube to work.
To get a proper image you must take a book of the subject. Prepare to find that to see it all you must understand quite well some electric field theory, electron physics differential equations and statistical mechanics.