The definition of anode and cathode is different for electrical devices such as diodes and vacuum tubes where the electrode naming is fixed and does not depend on the actual charge flow (current). Consequently, electrons leave the device through the anode and enter the device through the cathode. Since electrons have a negative charge, the direction of electron flow is opposite to the direction of conventional current. The currents outside the device are usually carried by electrons in a metal conductor. 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.Ĭonventional current depends not only on the direction the charge carriers move, but also the carriers' electric charge. An anode is an electrode of a device through which conventional current (positive charge) flows into the device from an external circuit, while a cathode is an electrode through which conventional current flows out of the device. The terms anode and cathode are not defined by the voltage polarity of electrodes but the direction of current through the electrode. Historically, the anode of a galvanic cell was also known as the zincode because it was usually composed of zinc. As a result of this, anions will tend to move towards the anode where they will undergo oxidation. In an electrolytic cell, the anode is the wire or plate upon which excess positive charge is imposed. In a galvanic cell the anode is the wire or plate having excess negative charge as a result of the oxidation reaction. In both a galvanic cell and an electrolytic cell, the anode is the electrode at which the oxidation reaction occurs. For example, the end of a household battery marked with a "-" (minus) is the anode. The direction of conventional current (the flow of positive charges) in a circuit is opposite to the direction of electron flow, so (negatively charged) electrons flow out the anode of a galvanic cell, into an outside or external circuit connected to the cell. A common mnemonic is ACID, for "anode current into device". This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. Note how electrons move out of the cell, and the conventional current moves into it in the opposite direction.Īn anode is an electrode of a polarized electrical device through which conventional current enters the device. Diagram of a zinc anode in a galvanic cell.
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