Generators and motors

Generators and motors are applications of electromagnetic induction. Figure 2illustrates a simple electric generator. 

Figure 2 A simple electric generator.

The crank represents a mechanical method of turning the loop of wire in a magnetic field. The change in magnetic flux through the loop generates an induced current; thus, the generator converts mechanical energy into electrical energy. The operation of a motor is similar to that of a generator but in reverse. The motor has similar physical components except that the electric current supplied to the loop exerts a torque, which turns the loop. The motor, therefore, converts electrical energy into mechanical energy.

Mutual inductance and self-inductance

Mutual inductance occurs when two circuits are arranged so that the change in current in one causes an emf to be induced in the other.

Imagine a simple circuit of a switch, a coil, and a battery. When the switch is closed, the current through the coil sets up a magnetic field. As the current is increasing, the magnetic flux through the coil is also changing. This changing magnetic flux generates an emf opposing that of the battery. This effect occurs only while the current is either increasing to its steady state value immediately after the switch is closed or decreasing to zero when the switch is opened. This effect is called self-inductance. The proportional constant between the self-induced emf and the time rate of change of the current is called inductance (L) and is given by 

The SI unit for inductance is the henry, and 1 henry = 1(Vs/A).

Using Faraday's law, inductance can be expressed in terms of the change of flux and current: