ELECTRIC MACHINES AND TRANSFORMERS
An electric machine is a device that can convert either mechanical energy to electric energy or electric energy to mechanical energy. Such a device is called a generator when it converts mechanical energy to electric energy. The device is called a motor when it converts electric energy to mechanical energy. Since an electric machine can convert power in either direction, such a machine can be used as either a generator or a motor. Thus, all motors and generators can be used to convert energy from one form to another, using the action of a magnetic field.
A transformer is a device that converts ac electric energy at one voltage level to ac electric energy at another voltage level. Transformers operate on the same principles as generators and motors.