The opposition to the flow of current in a circuit is called resistance . It is measured in ohms . The rate at which electrical energy is used up or dissipated is called power . There are two types of electrical current, direct and alternating . In direct current, the direction of the electron flow is constant.
Direct current is produced by batteries.
The direction of the electron flow is continually changing in alternating current. The Frequency of alternation of the regular household alternating current is 60 Hz. A capacitor is simply a pair of parallel metal plates. It stores electrical charge and acts like a frequency-dependent resistor in alternating current circuits. Its units are the Farad .