An electrolytic capacitor is often used to store large amounts of charge at relatively low voltages.
Structure of electrolytic capacitors | dielectric formation
This device, shown in Figure 1, consists of a metallic foil in contact with an electrolyte. Electrolyte is a solution that conducts electricity by virtue of the motion of ions contained in the solution. When a voltage is applied between the foil and the electrolyte, a thin layer of metal oxide (an insulator) is formed on the foil, and this layer serves as the dielectric.
Cause of large values of capacitance
Very large values of capacitance can be obtained in an electrolytic capacitor because the dielectric layer is very thin, and thus the plate separation is very small.
Polarity of Electrolytic capacitors
Electrolytic capacitors are not reversible as are many other capacitors – they have a polarity, which is indicated by positive and negative signs marked on the device. When electrolytic capacitors are used in circuits, the polarity must be aligned properly. If the polarity of the applied voltage is opposite that which is intended, the oxide layer is removed and the capacitor conducts electricity instead of storing charge.
Commercial capacitor designs
Three commercial capacitor designs include the following: (a) A tubular capacitor, whose plates are separated by paper and then rolled into a cylinder. (b) A high-voltage capacitor consisting of many parallel plates separated by insulating oil. (c) An electrolytic capacitor.