The electrode through which, by convention, electric current flows into a polarized electrical device. In physics, conventional current is regarded as a flow of positive charge – a definition that goes back to Michael Faraday (1791–1867), one of the pioneers of electrical science. (Conventional current is thus in the opposite direction to the flow of electrons.)
Contrary to many definitions that may be seen, the polarity of an anode can be positive or negative, depending on circumstances. In the case of a discharging cell or battery, the anode assumes a negative polarity – the (conventional) inward current being borne externally by electrons moving outward and continued internally by positive ions moving into the electrolyte. During charging of a secondary cell, the anode's role is reversed since it now receives conventional current from an external generator.
During electrolysis, the anode is the electrode to which negatively-charged ions (anions) are attracted. In a cathode ray tube (also known as electron tube), the anode is the positive terminal out from which electrons flow, i.e. where current flows into the device.
Related entries• cathode
• sacrificial anode
Related categories• ELECTRICITY AND MAGNETISM
• PHYSICAL CHEMISTRY
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