7.2.3 Electric Motors HT

In this lesson, we will delve into the working principle of electric motors and how the force acting on a conductor in a magnetic field leads to the rotation of the coil. 

Electric Motors

Electric motors are devices that convert electrical energy into mechanical motion. They operate based on the principle that a coil of wire carrying a current in a magnetic field experiences a rotational force.

• Electric motors utilise the interaction between a magnetic field and an electric current to generate rotational motion.
• The basic components of an electric motor include a coil of wire, a magnetic field, and a power source.

The Force on a Conductor in a Magnetic Field

• When a current-carrying conductor is placed in a magnetic field, a force is exerted on the conductor due to the motor effect.
• According to Fleming's left-hand rule, the force experienced by the conductor is perpendicular to both the magnetic field and the current direction.

Rotation of the Coil

In an electric motor, the conductor is typically in the form of a coil of wire.

• The motor effect causes the forces on different sections of the coil to act in different directions, resulting in a net rotational force.
• The coil, along with an axle or shaft, is mounted in such a way that it can rotate freely.

Commutator and Brushes

To ensure continuous rotation, electric motors use a commutator and brushes.

• The commutator is a device that reverses the direction of the current in the coil at specific points in each revolution.
• The brushes, usually made of carbon or graphite, maintain contact with the commutator and supply electrical current to the coil.

Generating Rotational Motion

• As the coil experiences the rotational force, it begins to rotate due to the interaction between the magnetic field and the current.
• The rotating motion of the coil is then transferred to a mechanical load, such as a fan, a wheel, or any other device that needs to be powered.

Conclusion

Electric motors are based on the principle that a coil of wire carrying a current in a magnetic field experiences a rotational force. This force on the conductor, known as the motor effect, results in the rotation of the coil.