Frequently asked in the IGCSE Physics are questions on the working principles of simple electric motors.

Electric motor works on a simple principle based on electromagnetism. 

• A simple electric motor is built so that a coil of wire connected to an electric circuit is free to rotate between two opposite magnetic poles. 
• When electric current flows, AB section of the coil experiences downward force, and CD section of the coil experiences upward force.
• The wire starts to rotate counterclockwise. 
• After half rotation, section CD is placed next to the north pole while section AB is placed next to the south pole. Since section CD still experiences an upward force, the direction of rotation will change.
• To make the rotation continuous, the commutator changes the direction of current flow every half rotation.
• With the change of the direction of current flow, the wire can rotate continuously in the same direction.

Example 1

Suggest three ways to increase the speed of rotation of the coil in the motor.

1. Increase the magnetic field by using stronger magnets or placing the two magnets closer.
2. Increase the current by increasing the voltage or decreasing the resistance by using wider wires.
3. Increase the number of turns on a coil.

Example 2

Suggest how to make the coil rotate in the other direction.

1. Reverse the direction of current flow. OR
2. Switch the location of north and south pole.

Example 3

In another motor, the magnets are curved and there is a piece of iron inside the coil. The iron increases the strength of the magnetic field through the coil.

Suggest how the curved magnets and piece of iron improve the performance of the electric motor.

1. The magnitude of the force increases because the iron core becomes magnetized. 
2. The magnetic field acts all the way around as the wire rotates.
3. Since the magnetic field acts all the way around, the force acts over a larger part of a cycle.

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