What is the function of a cathode in an electron tube?

The function of a cathode in an electron tube is to emit electrons when heated. In a typical electron tube, such as a thermionic emission device, the cathode is designed to be heated, usually by passing an electric current through it. As the cathode's temperature rises, it provides enough thermal energy for electrons to overcome the work function of the material, allowing them to be emitted into the vacuum within the tube.

This emission of electrons is critical for the operation of the electron tube, as the electrons can then be directed towards the anode or used in various applications, such as amplification or switching. The heating process and the subsequent release of electrons are key to the functioning of devices like vacuum tubes and cathode ray tubes, making this understanding vital in the study of electronics and physics.