Editing Anode (section)

==Charge flow==
The terms anode and [[cathode]] are not defined by the voltage polarity of electrodes, but are usually defined by the direction of current through the electrode. An anode usually is the electrode of a device through which [[conventional current]] (positive charge) flows into the device from an external circuit, while a cathode usually is the electrode through which conventional current flows out of the device.

In general, if the current through the electrodes reverses direction, as occurs for example in a [[rechargeable battery]] when it is being charged, the roles of the electrodes as anode and cathode are reversed.<ref name="Inside a Tube">{{cite web |title=Inside a Tube |url=https://web.archive.org/web/20101007201649/http://pentalabs.com/tubeworks.html#INSIDE |publisher=Penta Labs |access-date=31 December 2024}}</ref> However, the definition of anode and cathode is different for electrical devices such as [[diode]]s and [[vacuum tube]]s where the electrode naming is fixed and does not depend on the actual charge flow (current). These devices usually allow substantial current flow in one direction but negligible current in the other direction. Therefore, the electrodes are named based on the direction of this "forward" current. In a diode the anode is the terminal through which current enters and the cathode is the terminal through which current leaves, when the diode is [[forward bias]]ed. The names of the electrodes do not change in cases where reverse current flows through the device. Similarly, in a vacuum tube only one electrode can [[Thermionic emission|thermionically emit]] electrons into the evacuated tube, so electrons can only enter the device from the external circuit through the [[Hot cathode|heated electrode]]. Therefore, this electrode is permanently named the cathode, and the electrode through which the electrons exit the tube is named the anode.<ref name="Inside a Tube"/>

Conventional current depends not only on the direction the [[charge carrier]]s move, but also the carriers' [[electric charge]]. The currents outside the device are usually carried by [[electron]]s in a metal conductor. Since electrons have a negative charge, the direction of electron flow is opposite to the direction of conventional current.  Consequently, electrons leave the device through the anode and enter the device through the cathode.<ref name="Inside a Tube"/>