What is "anode"

Anode \An"ode\, n. [Gr. ? up + ? way.] (Elec.) The positive pole of an electric battery, or more strictly the electrode by which the current enters the electrolyte on its way to the other pole; -- opposed to cathode.

1834, coined from Greek anodos "way up," from ana "up" (see ana-) + hodos "way" (see cede). Proposed by the Rev. William Whewell (1794-1866), English polymath, and published by English chemist and physicist Michael Faraday (1791-1867). So called from the path the electrical current was thought to take. Related: Anodic.

n. 1 (context electricity English) An electrode, of a cell or other electrically polarized device, through which a positive current of electricity flows inwards (and thus, electrons flow outwards). It usually, but not always, has a negative voltage. 2 (context chemistry by extension English) The electrode at which chemical oxidation of anions takes place, usually resulting in the erosion of metal from the electrode. 3 (context electronics English) The electrode which collects electrons emitted by the cathode in a http://en.wikipedia.org/wiki/vacuum%20tube or http://en.wikipedia.org/wiki/gas-filled%20tube. 4 (context electronics English) That electrode of a semiconductor device which is connected to the p-type material of a p-n junction.

1. n. a positively charged electrode by which electrons leave an electrical device [ant: cathode]

2. the negatively charged terminal of a voltaic cell or storage battery that supplies current [ant: cathode]

An anode is an electrode through which conventional current flows into a polarized electrical device. A common mnemonic is ACID for "anode current into device". The direction of (positive) electric current is opposite to the direction of electron flow: (negatively charged) electrons flow out the anode to the outside circuit.

The polarity of voltage on an anode with respect to an associated cathode varies depending on the device type and on its operating mode. In the following examples, the anode is negative in a device that provides power, and positive in a device that consumes power:

• In a discharging battery or galvanic cell (diagram at right), the anode is the negative terminal because it is where current flows into "the device" (i.e. the battery cell). This inward current is carried externally by electrons moving outwards, negative charge flowing in one direction being electrically equivalent to positive charge flowing in the opposite direction.
• In a recharging battery, or an electrolytic cell, the anode is the positive terminal, which receives current from an external generator. The current through a recharging battery is opposite to the direction of current during discharge; in other words, the electrode which was the cathode during battery discharge becomes the anode while the battery is recharging.
• In a diode, the anode is the positive terminal at the tail of the arrow symbol (flat side of the triangle), where current flows into the device. Note electrode naming for diodes is always based on the direction of the forward current (that of the arrow, in which the current flows "most easily"), even for types such as Zener diodes or solar cells where the current of interest is the reverse current.
• In a cathode ray tube, the anode is the positive terminal where electrons flow out of the device, i.e., where positive electric current flows in.