Electrolyte-capacitors

An electrolyte capacitor is obtained by passing a direct current between two sheets of aluminium foils
with a suitable electrolyte like aluminium borate between the foils. Due to electrolysis, a very thin film of thickness of the order of 10^-6cm of aluminium oxide is formed on the anode plate and acts as the dielectric between the plates. This oxide layer is very thin, so that capacity of this capacitor becomes very high. Care must be taken to connect this capacitor with proper polarity in a circuit. Otherwise the oxide film will break down. For this reason, in an electrolyte capacitor the polarity of terminals will be indicated.
These capacitors are widely used when high capacitances are required.