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.

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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.

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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.

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Chemistry: Chemistry (in Greek: χημεία) is the science of matter that deals with the composition, structure, and properties of substances and with the transformations that they undergo. In the study of matter, chemistry also investigates its interactions with energy and itself (se...

Electrode: An electrode is a conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte or a vacuum). The word was coined by the scientist Michael Faraday from the Greek words elektron (meaning amber, whence the word electricity is derived) and hodos, a way ....

Electrochemical cell: An electrochemical cell is a setup used for creating an electromotive force in a conductor separating two reactions. The current is caused by the reactions releasing and accepting electrons in to the different ends of the conductor. The most common example of an electrochemical cell is a standard 1....