Electric motors are devices that convert electrical energy into mechanical energy, usually in the form of rotational motion. In simple terms, they are devices that use electric power to generate motive power.
Not only do electric motors provide a simple and efficient means of generating high levels of drive output, but they are also easy to make smaller, allowing them to be incorporated into other machinery and equipment. As a result, they are found in a wide variety of applications in both industry and daily life.
Principle of operation
Do you remember being taught Fleming's left-hand rule at school? Electric motors are an application of this rule, with the force generated by electric current flowing through a coil in the presence of a magnetic field causing the motor shaft to rotate.
In the diagram below, Fleming's left-hand rule tells us that an upward force is generated when current flows perpendicular to the magnetic field from the magnet*.
Magnetic field: A region in which a magnetic force is present (directed from the north (N) to the south (S) pole of the magnet).
How rotation is achieved in an electric motor
In the case of a brushed DC electric motor*1, for example, this force can be used to sustain continuous rotation by reversing the direction of current flow at each half-turn of the coil (which is achieved by means of the brushes and commutator*2)
DC motor: A motor powered by direct current (DC)
Brushes and commutator: Used together, these reverse the direction of current flow each time the motor shaft makes half a turn.
History of electric motors
The British scientist Michael Faraday is recognized as being particularly influential among the many scientists from the 19th century who played a part in the invention and development of electric motors. In 1821, Faraday conducted the successful experiment in which the rotation of a wire was achieved using a magnet together with a magnetic field generated by an electric current. He went on to invent the law of magnetic induction in 1831, laying the groundwork for significant progress in electric motors and generators.
Over time, many other types of electric motors were devised, along with structures that can be considered the archetypal DC motor.
Subsequently, in 1872, the practical electric motor was not so much invented as discovered when one of the generators exhibited at the Vienna World's Fair started rotating on its own after being accidentally connected to another generator. This led people to realize that the way generators worked could also be used in motors. The rapid growth that followed in the practical use of generators was such that they became a mainstay of many industries in the 20th century.