electron gun?

[SataN]

hi, i was wondering if any1 new anything about thermionic emission and in particular the electron gun. i just wanted to know how the potential difference between the filament and the anode is created. i don't understand!!

also what makes something positive i.e. this metal plate is negatively charged and this one is positively charged?

[Qfwfq]

Hmmm... I'm not sure what to explain to you and what not to. Perhaps you know already that a DC battery has a positive(+) pole and a negative(-) pole. Well, these poles are each said to be charged positively and negatively and if you connect them with other conductors, so will these be charged accordingly. So we also say that there is a potential difference between them, just another way of saying they are differently charged.

All right, in a metallic conductor only the electrons (-) are free to move around. The positive charges are inside the atoms and they stay still. It's a bit more complicated in semiconductors. A metal plate therefore has more electrons when it is negatively charged and less when positively charged. Anode is just a Greek name for the positively charged metal plate.

The potential difference you are asking about is typically a very strong one, stronger than just a battery could create, anyway it isn't created by the device itself but outside it, by a special circuit, and passed through the terminals on the device's socket. The current that heats the filament is also supplied through this socket. The heat helps to make electrons jump out of the conductor, much like water molecules come out of hot water making steam.

According to what you know and don't, what you understand and don't, ask more questions...

[SataN]

ok, that partly explains it, thanks, so, the anode is connected to the positive terminal of the high volatage unit and the filament to the negative terminal, the anode becomes positive because electrons are moving from it to the positive terminal and the filament negative because electrons are moving from the -ve termainal to it? and thus the anode is positive relative to the filament?

[Qfwfq]

I can see that you're understanding. If my explanation is still partial, ask specific questions...