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The electron gun

If a plate (the cathode) is heated in a vacuum electrons are "boiled" off its surface. If a positively charged plate (the anode) is put near the cathode the electrons will be attracted towards it.

A beam of electrons therefore travels across between the cathode and the anode and this is called a cathode ray. If the anode is cylindrical the electron beam will pass through the centre and out the other side. This is called an electron gun.

If the potential difference between the cathode and the anode is V, the mass of the electron (m) and the charge on the electron (e) the velocity with which the electrons emerge from the electron gun is:

Electron velocity = [2eV/m]1/2

Properties of electron beams - cathode rays

(b) they could be deflected by both electric and magnetic fields
(c) they moved in circles in magnetic fields and in parabolas in electric fields
(d) they could cause fluorescence
(e) they possessed kinetic energy which could be changed to heat when they were brought to rest
(f) they could produce X rays if they had sufficiently high energy

© Keith Gibbs 2011