Electrolytic capacitor An insulating dielectric film is formed on the surface by electrolysis by putting an electrode of a metal, for example aluminum, in the electrolyte. Capacitors made in this way are called electrolytic capacitors. It is easy to make small and large capacity, but it is mainly used for low frequency or commercial frequency circuits because high frequency loss is large. A film having both the cathode and the anode is called an alternating current electrolytic capacitor, and is used for starting a single-phase induction motor.