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Encyclopedia > Cathode
Diagram of a copper cathode in a Daniell's cell.
Diagram of a copper cathode in a Daniell's cell.

The word cathode comes from the Greekword κάθοδος meaning, 'going down'. A cathode is the electrode at which electrons enter an electric power source such as a galvanic cell or a battery. However, for an electric power sink (load) such as an electrolytic cell or a diode, electrons flow out of the cathode. The other charged electrode in the same cell or device is the anode. Wikipedia does not have an article with this exact name. ... Wikipedia does not have an article with this exact name. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic brown Atomic mass 63. ... The Galvanic cell, named after Luigi Galvani, consists of two metals connected by an electrolyte which forms a salt bridge between the metals. ... Greek (, IPA — Hellenic) is an Indo-European language with a documented history of 3,500 years. ... An electrode is a conductor used to make contact with a nonmetallic part of a circuit (e. ... Properties The electron is a fundamental subatomic particle that carries a negative electric charge. ... The Galvanic cell, named after Luigi Galvani, consists of two metals connected by an electrolyte which forms a salt bridge between the metals. ... The word battery has a number of senses, most of which are discussed in articles cited below. ... Electrolytic cells are composed of an electrolyte (usually water or another solvent capable of dissolving various ions of interest), a cathode and an anode. ... Types of diodes In electronics, a diode is a component that restricts the direction of movement of charge carriers. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... An electrode is a conductor used to make contact with a nonmetallic part of a circuit (e. ... Diagram of a zinc anode in a Daniells cell. ...


When dealing with devices which have a definite cathode and anode, it is important to remember that the direction of an electric current is always opposite to the direction of flow of electrons. This is because electric current is defined as the flow of positive charges while electrons are negatively charged. Diagram of a zinc anode in a Daniells cell. ... // Electric current is the flow of electric charge. ... Properties The electron is a fundamental subatomic particle that carries a negative electric charge. ... // Electric current is the flow of electric charge. ... ‹ The template below has been proposed for deletion. ... Properties The electron is a fundamental subatomic particle that carries a negative electric charge. ...

Contents


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 (electrons are added to cations to complete the valence shell or bond). Multicolored chemicals are frequent hallmarks of chemistry. ... An electrode is a conductor used to make contact with a nonmetallic part of a circuit (e. ... An electrochemical cell is a setup used for creating an electromotive force(voltage) in a conductor separating two reactions. ... The most fundamental reactions in chemistry are the redox processes. ...


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. Electrolytic cells are composed of an electrolyte (usually water or another solvent capable of dissolving various ions of interest), a cathode and an anode. ...


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. The Galvanic cell, named after Luigi Galvani, consists of two metals connected by an electrolyte which forms a salt bridge between the metals. ...


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. A Superconductor demonstrating the Meissner Effect. ... The field of electronics is the study and use of systems that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves and semiconductors. ...


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. In electronics, a vacuum tube (U.S. and Canadian English) or (thermionic) valve (outside North America) is a device generally used to amplify, or otherwise modify, a signal by controlling the movement of electrons in an evacuated space. ... Thermionic emission (archaically known as the Edison effect) is the flow of electrons from a metal or metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface. ... Also known as Fowler-Nordheim tunneling, field emission is a form of quantum tunneling in which electrons pass through a barrier in the presence of a high electric field. ... An electrode is a conductor used to make contact with a nonmetallic part of a circuit (e. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... The photoelectric effect is the emission of electrons from a surface (usually metallic) upon exposure to, and absorption of, electromagnetic radiation (such as visible light and ultraviolet radiation) that is above the threshold frequency particular to each type of surface. ...


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(s) in cathode ray tubes in many television sets and computer monitors. Hot electron emitters are also are used as the electrodes in fluorescent lamps. Also known as Fowler-Nordheim tunneling, field emission is a form of quantum tunneling in which electrons pass through a barrier in the presence of a high electric field. ... Note: Principles are mostly the same for cold cathode ion sources as in particle accelerators to create electrons. ... Note: Principals are mostly the same for hot cathode ion sources in particle accelerators to create electrons The Hot filament ionization gauge sometimes called a hot filament and hot cathode , is the most widely used vacuum (negative pressure) measuring device for the region from 10-1 to 10-9 pascals. ... A filament is a fine, thinly spun thread, fiber, or wire. ... The cathode ray tube or CRT, invented by Karl Ferdinand Braun, is the display device used in most computer displays, televisions and oscilloscopes. ... A compact fluorescent lamp A fluorescent lamp is a type of electric lamp that excites argon and mercury vapor to create luminescence. ...


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 (N-doped for negative charge carrier ions). (The anode side has a base positive charge at this point, since it supplied electrons to the recombinant region and the doped ions are short of a full valence shell of electrons). 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 (electrons flow from N-doped to P-doped when the bias is overcome). Unlike a typical diode, there is no fixed anode or cathode in a zener diode. Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide. ... Types of diodes In electronics, a diode is a component that restricts the direction of movement of charge carriers. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... Diagram of a zinc anode in a Daniells cell. ...


See also

Diagram of a zinc anode in a Daniells cell. ... Electrolytic cells are composed of an electrolyte (usually water or another solvent capable of dissolving various ions of interest), a cathode and an anode. ... An electrode is a conductor used to make contact with a nonmetallic part of a circuit (e. ... Four double-A (AA) rechargeable batteries In science and technology, a battery is a device that stores chemical energy and makes it available in an electrical form. ... Cathode ray tube employing electromagnetic focus and deflection Cutaway rendering of a color CRT The cathode ray tube or CRT, invented by Karl Ferdinand Braun, is the display device that was traditionally used in most computer displays, video monitors, televisions, radar displays and oscilloscopes. ... Electron tube can be used to describe either of two things: vacuum tube gas filled tube This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... In chemistry and manufacturing, electrolysis is a method of separating bonded elements and compounds by passing an electric current through them. ...

External links

  • The Cathode Ray Tube site
  • Valence Technologies Inc. battery education page

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knitty.com (681 words)
Vibrant colors, extradeep ribbing, and a big bold collar make Cathode an excellent way to jolt yourself out of the winter blues.
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He noticed that the cathode rays were emitted perpendicular with respect to the surface of the cathode on the contrary to the shafts which propagate in all directions.
When the A one is the cathode the spectroscope should record the light of the particles getting close (the Doppler shift should occur) When the B one is the cathode the spectroscope recorded light is caused bby the particles moving perpendicular with the respect to the spectroscope (there should be no Doppler shift).
The cathode rays emitted at the cathode are passing through a small slot in the anode and through a wire net (the net has connections with the anode, and it's task was to screen the rest of the tube from electrode influence - electric field was only between the anode and the cathode).
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