Electrode Whewell at Faraday's request). The anode is now defined as the electrode at which electrons leave the cell and oxidation occurs (indicated by a minus symbol, "−"), and the cathode as the electrode at which electrons enter the cell and reduction occurs (indicated by a plus symbol, "+"). Each electrode may become either the anode or the cathode depending on the direction of current through the cell. A bipolar electrode is an electrode that functions as the anode of one cell and the cathode of another cell. A primary cell is a special type of electrochemical cell in which the
Plate electrode tube envelope and is cooled by radiation cooling, forced air or water. A problem in early vacuum tubes was "secondary emission"; electrons striking the plate could knock other electrons out of the metal surface. In some tubes such as tetrodes these "secondary electrons" could be absorbed by other electrods such as grids in the tube, resulting in a current out of the plate. This current could cause the plate circuit to have negative resistance, which could cause unwanted parasitic oscillations. To prevent this most plates in modern tubes are given a chemical coating which reduces secondary emission. Plate electrode A