Cathode
A cathode is the electrode at which
electrons go into a cell, tube or diode, whether driven externally or internally. It comes from the Greek word
????d?? meaning, 'descent'. The other charged electrode in the same cell or device is the
anode.
Encyclopedia
A
cathode is the electrode at which
electrons go into a cell, tube or diode, whether driven externally or internally. It comes from the Greek word
????d?? meaning, 'descent'. The other charged electrode in the same cell or device is the
anode.
Flow of electrons
The flow of electrons is
always from
anode–to–cathode outside of the cell or device, and from
cathode–to–anode inside the cell or device, regardless of the cell or device type. Inside a chemical cell, ions are carrying the electrons but the flow is still from
cathode–to–anode inside the cell.
Chemistry cathode
In
chemistry, a
cathode is the electrode of an
electrochemical cell at which reduction occurs .
Electrolytic cell
In an electrolytic cell, the cathode is where the negative polarity is applied to drive the cell. Common results of reduction at the cathode are hydrogen gas or pure metal from metal ions.
Galvanic cell
In a
galvanic cell, the cathode is where the positive
pole is connected to allow the circuit to be completed: as the anode of the galvanic cell gives off electrons, they return from the circuit into the cell through the cathode.
Electroplating metal cathode
When metal ions are reduced from ionic solution onto the cathode, they form a pure metal surface on the cathode. Items to be plated with pure metal are attached to and become part of the cathode in the electrolytic solution.
Electronics and physics cathode
In
physics or
electronics, a
cathode is an electrode that emits electrons into the device.
Vacuum tubes
In a
vacuum tube or other electronic vacuum system, the cathode emits free 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.
Cold cathodes and hot cathodes
Cathodes used for field emission in vacuum tubes are called
cold cathodes. Heated electrodes or
hot cathodes, frequently called filaments, are much more common. Most radios and television sets prior to the 1970s used filament-heated-cathode electron tubes for signal selection and processing; to this day, a hot cathode forms the source of the electron beam in
cathode ray tubes in many television sets and computer monitors. Hot electron emitters are also are used as the electrodes in
fluorescent lamps.
Diodes
In a
semiconductor diode, the cathode is the N–doped layer of the PN junction. Initially, the N-doped layer supplies 'holes' to flow into the junction. The holes given by the N-doped layer combine with
electrons supplied from the P-doped layer. The electrons and holes combining creates a 'depleted' zone at the junction, leaving behind in the cathode a layer of negative ions which gives a base negative charge to the cathode side of device . . As a negative charge is applied to the cathode from the circuit external to the diode, more N-doped ions are able to supply 'holes' to the recombinant region and the diode becomes conductive, which allows electrons to flow though the diode from the cathode to the anode . Unlike a typical diode, there is no fixed anode or cathode in a zener diode.
See also
In chemistry and manufacturing,
electrolysis is a method of separating bonde...
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