Cathode (Encyclopedia of Science)
A cathode is one of the two electrodes used either in a vacuum tube or in an electrochemical cell. An electrode is the part (pole) of a vacuum tube or cell through which electricity moves into or out of the system. The other pole of the system is referred to as the anode.
A vacuum tube is a hollow glass cylinder from which as much air as possible has been removed. In a vacuum tube, the cathode is the negative electrode. It has more electrons on its surface than does the other electrode, the anode. Electrons can accumulate on the surface of a cathode for various reasons. For example, in some vacuum tubes, the cathode is heated to a high temperature to remove electrons from atoms that make up the cathode. The free electrons are then able to travel from the cathode to the anode. These streams of electrons are known as cathode rays, and the tubes in which they are produced are called cathode-ray tubes (CRTs). CRTs are widely used as oscilloscopes (which measure changes in electrical voltage over time), television tubes, and computer monitors.
Electrochemical cells are devices for turning chemical energy into electrical energy or, alternatively, changing electrical energy into chemical energy. Electrochemical cells are of two types: voltaic cells (also called galvanic cells) and...
(The entire section is 465 words.)
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