Electrical engineers like to reduce diagrams of electrical circuits, no matter how complicated, to an "equivalent circuit" consisting of a network of just "four" different types of component. These four basic components are "emfs", "resistors", "capacitors", and "inductors". An inductor is usually represented by a little solenoid in circuit diagrams. In practice, inductors generally consist of short air-cored solenoids wound from enameled copper wire.