Cathode

In chemistry a cathode is the electrode of an electrochemical cell at which reduction occurs. It comes from the Greek word κάθοδος meaning, 'going down'. In an electrolytic cell the cathode is negatively charged and in a galvanic cell the cathode is positively charged. The oppositely charged electrode in that same cell is referred to as the anode.

Related Topics:
Chemistry - Electrode - Electrochemical cell - Reduction - Greek - Electrolytic cell - Galvanic cell - Anode

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In physics a cathode is an electrode in a vacuum tube or other vacuum system which produces electrons. Electrons are extracted from metal electrodes either by heating the electrode, causing thermionic emission, or by applying a strong electric field and causing field emission. Electrons can also be emitted from the electrodes of certain metals when light of frequency greater than the threshold frequency falls on it. This is called photoelectric emission.

Related Topics:
Physics - Vacuum tube - Thermionic emission - Field emission - Electrode - Frequency - Photoelectric emission

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Cathodes used for field emission in vacuum tubes are called cold cathodes. Heated electrodes, frequently called filaments, are much more common. Most radios and television sets prior to the 1970s use filament heated cathode electron tubes for signal selection and processing as do many television sets to this day, forming the source of the electron beam in cathode ray tubes. Hot electron emitters are also are used as the electrodes in fluorescent lamps.

Related Topics:
Cold cathodes - Filaments - Cathode ray tubes - Fluorescent lamps

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