# Electron gun - electron in cylindrical anode

In an electron gun, the heating filament heats the cathode, releasing electrons by thermionic emission. I've read that "electrons are negatively charged particles and the positively charged cylindrical anode develops a strong electric field that exerts a force on the electrons, accelerating them along the tube". However, I don't think that this explanation is very clear, and I was wondering specifically how the "strong electric field" inside the cylindrical anode is able to accelerate the electrons?

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Just to clarify your question a little bit, are you asking how an electric field accelerates a charged particle? Or are you asking if the cylindrical symmetry of the anode should result in zero electric field? –  Colin K Jun 16 '11 at 18:11

## 2 Answers

any electric field will accelerate electrons, according to the Lorentz force law:

$\vec{F} = q \vec{E} + \vec{v} \times \vec{B}$,

where q is the charge of the electron, and $\vec{E}$ is the electric field. I assume there is no magnetic field in this example, so the second term is zero.

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The acceleration mostly happens in the gap between the cylindrical anode's edge and the cathode. The field becomes uniform inside a relatively long cylinder so there is no acceleration there. I am sure others can elaborate this but I think I found the important part of your question. Some book made an error.

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