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Diagram of a zinc anode in a galvanic cell.
Diagram of a zinc anode in a galvanic cell. Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 The Galvanic cell, named after Luigi Galvani, consists of two different metals connected by a Salt bridge or a porous disk between the individual half-cells

An anode is an electrode through which (positive) electric current flows into a polarized electrical device. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. Mnemonic: ACID (Anode Current Into Device). Electrons flow in the opposite direction to the positive electric current.

A widespread misconception is that anode polarity is always positive. This is often inferred from the correct fact that in all electrochemical devices negatively charged anions move towards the anode and/or positively charged cations move away from it. Anode polarity is not always positive but depends on the device type, and sometimes even in which mode it operates, as determined by the above electric current direction-based universal definition.

Examples:

A polarised electric device always has at least two electrodes - one through which positive electric current charge flows into the device and one through which the current flows out. The electrode that electric current flows into the device through is by definition always the anode, the current out electrode is always the cathode. A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device Again note that the electron flow is OPPOSITE to the positive electric current charge flow, which has been a source of confusion.

Contents

Etymology

The word was coined in 1834 from the Greek ἄνοδος (anodos), 'way up', by William Whewell, who had been consulted[1] by Michael Faraday over some new names needed to complete a paper on the recently discovered process of electrolysis. Year 1834 ( MDCCCXXXIV) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian Calendar (or a Common Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly William Whewell ( May 24, 1794 &ndash March 6, 1866) was an English Polymath, Scientist, Anglican Priest Michael Faraday, FRS ( September 22 1791 – August 25 1867) was an English In chemistry and manufacturing electrolysis is a method of separating chemically bonded elements and compounds by passing an Electric current In that paper Faraday explained that when an electrolytic cell is oriented so that electric current traverses the "decomposing body" (electrolyte) in a direction "from East to West, or, which will strengthen this help to the memory, that in which the sun appears to move", the anode is where the current enters the electrolyte, on the East side: "ano upwards, odos a way ; the way which the sun rises" ([2], reprinted in [3]).

The use of 'East' to mean the 'in' direction (actually 'in' → 'East' → 'sunrise' → 'up') may appear unnecessarily contrived. Previously, as related in the first reference cited above, Faraday had used the more straightforward term "eisode" (the doorway where the current enters). His motivation for changing it to something meaning 'the East electrode' (other candidates had been "eastode", "oriode" and "anatolode") was to make it immune to a possible later change in the direction convention for current, whose exact nature was not known at the time. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. The reference he used to this effect was the Earth's magnetic field direction, which at that time was believed to be invariant. He fundamentally defined his arbitrary orientation for the cell as being that in which the internal current would run parallel to and in the same direction as a hypothetical magnetizing current loop around the local line of latitude which would induce a magnetic dipole field oriented like the Earth's. A solenoid is a three-dimensional Coil. In Physics, the term solenoid refers to a loop of wire often wrapped around a Metallic core which In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a This made the internal current East to West as previously mentioned, but in the event of a later convention change it would have become West to East, so that the East electrode would not have been the 'way in' any more. Therefore "eisode" would have become inappropriate, whereas "anode" meaning 'East electrode' would have remained correct with respect to the unchanged direction of the actual phenomenon underlying the current, then unknown but, he thought, unambiguously defined by the magnetic reference. In retrospect the name change was unfortunate, not only because the Greek roots alone do not reveal the anode's function any more, but more importantly because, as we now know, the Earth's magnetic field direction on which the "anode" term is based is subject to reversals whereas the current direction convention on which the "eisode" term was based has no reason to change in the future. A geomagnetic reversal is a change in the orientation of Earth's magnetic field such that the positions of magnetic north and magnetic south become interchanged Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere.

Since the later discovery of the electron, an easier to remember, and more durably correct technically although historically false, etymology has been suggested: anode, from the Greek anodos, 'way up', 'the way (up) out of the cell (or other device) for electrons'. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J

Flow of electrons

The flow of electrons is always from anode to cathode outside of the cell or device, regardless of the cell or device type and operating mode, with the exception of diodes, where electrode naming always assumes current flows in the forward direction (that of the arrow symbol), i. e. , electrons flow in the opposite direction, even when the diode reverse-conducts either by accident (breakdown of a normal diode) or by design (breakdown of a Zener diode, photo-current of a photodiode or solar cell).

Electrolytic anode

In electrochemistry, the anode is where oxidation occurs, and is the positive polarity contact in an electrolytic cell. Electrochemistry is a branch of Chemistry that studies Chemical reactions which take place in a Solution at the interface of an electron conductor Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state An electrolytic cell decomposes chemical compounds by means of electrical energy in a process called Electrolysis; the Greek word Lysis means to break up At the anode, anions (negative ions) are forced by the electrical potential to react chemically and give off electrons (oxidation) which then flow up and into the driving circuit. An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge

Battery or galvanic cell anode

In a battery or galvanic cell, the anode is the negative electrode from which electrons flow out towards the external part of the circuit. In electronics a battery is a combination of two or more Electrochemical cells which store chemical Energy which can be converted into electrical energy The Galvanic cell, named after Luigi Galvani, consists of two different metals connected by a Salt bridge or a porous disk between the individual half-cells Internally the positively charged cations are flowing away from the anode (even though it is negative and therefore would be expected to attract them, this is due to electrode potential relative to the electrolyte solution being different for the anode and cathode metal/electrolyte systems); but, external to the cell in the circuit, electrons are being pushed out through the negative contact and thus through the circuit by the voltage potential as would be expected. In Electrochemistry, the standard electrode potential, abbreviated Eo E0 or EO (with a superscript Plimsoll character pronounced Note: in a galvanic cell, contrary to what occurs in an electrolytic cell, no anions flow to the anode, the internal current being entirely accounted for by the cations flowing away from it (cf drawing).

In the United States, many battery manufacturers regard the positive electrode as the anode, particularly in their technical literature. Though technically incorrect, it does resolve the problem of which electrode is the anode in a secondary (or rechargeable) cell. Using the traditional definition, the anode switches ends between charge and discharge cycles.

Vacuum tube anode

In electronic vacuum devices such as a cathode ray tube, the anode is the positively charged electron collector. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or In a tube, the anode is a charged positive plate that collects the electrons emitted by the cathode through electric attraction. It also accelerates the flow of these electrons.

Diode anode

In a semiconductor diode, the anode is the P-doped layer which initially supplies holes to the junction. A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes An electron hole is the conceptual and mathematical Opposite of an Electron, useful in the study of Physics and Chemistry. In the junction region, the holes supplied by the anode combine with electrons supplied from the N-doped region, creating a depleted zone. As the P-doped layer supplies holes to the depleted region, negative dope ions are left behind in the P-doped layer ('P' for positive charge-carrier ions). This creates a base negative charge on the anode. When a positive voltage is applied to anode of the diode from the circuit, more holes are able to be transferred to the depleted region, and this causes the diode to become conductive, allowing current to flow through the circuit. An electron hole is the conceptual and mathematical Opposite of an Electron, useful in the study of Physics and Chemistry. The terms anode and cathode should not be applied to a zener diode, since it allows flow in either direction, depending on the polarity of the applied potential (i. e. voltage).

Sacrificial anode

In cathodic protection, a metal anode that is more reactive to the corrosive environment of the system to be protected is electrically linked to the protected system, and partially corrodes or dissolves, which protects the metal of the system it is connected to. Cathodic protection ( CP) is a technique to control the Corrosion of a metal surface by making it work as a Cathode of an Electrochemical Corrosion means the breaking down of essential properties in a material due to Chemical reactions with its surroundings As an example, an iron or steel ship's hull may be protected by a zinc sacrificial anode, which will dissolve into the seawater and prevent the hull from being corroded. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 A hull is the body of a Ship or Boat. It is a central concept in floating vessels as it provides the Buoyancy that keeps the vessel from sinking A sacrificial anode, or sacrificial rod, is a metallic Anode used in Cathodic protection where it is intended to be dissolved to protect other metallic Sacrificial anodes are particularly needed for systems where a static charge is generated by the action of flowing liquids, such as pipelines and watercraft. Electrostatics is the branch of Science that deals with the Phenomena arising from what seems to be stationary Electric charges Since Classical

At least one anode is found in tank-type hot water heaters. The anode should be removed and checked after 5 years(sooner if there is a sodium based water softner inline), and replaced if 6 inches (15 cm) or more of bare wire is showing. This will greatly extend the life of the tank.

Water heater anode information

Related antonym

The opposite of an anode is a cathode. A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device When the current through the device is reversed, the electrodes switch functions, so anode becomes cathode, while cathode becomes anode, as long as the reversed current is applied, with the exception of diodes where electrode naming is always based on the forward current direction. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e

See also

References

  1. ^ Ross, S, Faraday Consults the Scholars: The Origins of the Terms of Electrochemistry in Notes and Records of the Royal Society of London (1938-1996), Volume 16, Number 2 / 1961, Pages: 187 - 220, [1] consulted 2006-12-22
  2. ^ Faraday, Michael, Experimental Researches in Electricity. A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device Anodizing, or anodising, is an electrolytic Passivation process used to increase the thickness of the natural Oxide layer on the surface of metal WikipediaNaming In electronics a battery is a combination of two or more Electrochemical cells which store chemical Energy which can be converted into electrical energy Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes Cathodic protection ( CP) is a technique to control the Corrosion of a metal surface by making it work as a Cathode of an Electrochemical In chemistry and manufacturing electrolysis is a method of separating chemically bonded elements and compounds by passing an Electric current The Galvanic cell, named after Luigi Galvani, consists of two different metals connected by a Salt bridge or a porous disk between the individual half-cells Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state A primary cell is any kind of Electrochemical cell in which the electrochemical reaction of interest is not reversible so used in Disposable Seventh Series, Philosophical Transactions of the Royal Society of London (1776-1886), Volume 124, 01 Jan 1834, Page 77, [2] consulted 2006-12-27 (in which Faraday introduces the words electrode, anode, cathode, anion, cation, electrolyte, electrolyze)
  3. ^ Faraday, Michael, Experimental Researches in Electricity, Volume 1, 1849, reprint of series 1 to 14, freely accessible Gutenberg. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge An electrolyte is any substance containing free Ions that behaves as an electrically conductive medium In chemistry and manufacturing electrolysis is a method of separating chemically bonded elements and compounds by passing an Electric current org transcript [3] consulted 2007-01-11

External links

Dictionary

anode

-noun

  1. the electrode of an electrochemical cell at which oxidation occurs
  2. the positive terminal of an electrolytic cell
  3. the negative terminal of a galvanic cell
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