Cathode Rays and Thermionic Emmision


Is electron beam the same as cathode ray? Is there any cathode ray which is not composed of electrons?

What is the meaning of thermionic emmision?

Is there any method to produce electrons besides thermionic emmision?

How does cathode in a cathode ray tube produce electrons? From the accumulation of negative charges due to voltage supply or by heating up of cathode and emit electrons?


Electron beams and cathode rays are the same thing. Before we knew about electrons the name cathode ray was used.

Thermionic emission is the mechanism by which electrons are set free from the metal structure of the cathode. By heating the cathode the electrons are given enough energy to break the bond holding them in the metal.

Electrons may be freed from material by other means than thermionic emission. The photo-electric effect is one way. Also electrons can be emitted from the nucleus of an atom by beta decay.

In the CRT, heating the cathode gives the electrons enough energy to become free of the surface. If there were no voltage applied the freed electrons would just form a cloud around the cathode. The application of the voltage causes the electrons to stream away from the cathode in a ray or beam. Of course those that leave the cathode must eventually be replaced from the power supply.