Cathode
[1] In an electric circuit, the
negative terminal. Electrons leave at this terminal.
[2] In an electronic tube or valve, an electrode through which a primary stream of electrons enters the inter-electrode space. During conduction, the
cathode is negative with respect to the
anode. Such a
cathode may be cold, electron emission being due to electric fields, photo-emission, or impact by other particles, or thermionic, where the
cathode is heated by some means.
[3] In a semiconductor diode, the electrode to which the forward current flows.
[4] In a thyristor, the electrode by which current leaves the thyristor when it is in the ON state.
[5] In a
light-emitting diode (LED), the electrode to which forward current flows within the devie.
[6] In electrolytic applications, the electrode at which positive ions are discharged, or negative ions formed.
