Electric Motors

When a coil of wire carries an electric current in a magnetic field, it experiences a force which can cause the coil of wire to rotate. This is how electric motors function.

The diagram below shows a simple dc electric motor.

We use a coil of wire that is free to rotate between two opposite magnetic poles.

Each end of the coil is connected to a split ring commutator and each side of the commutator is connected to the opposite sides of a direct current (DC) power supply.

How the DC Electric Motor works

1. The flowing current will create a magnetic field around the coil.

2. The magnetic field produced by the current will interact with the magnetic field produced by the permanent magnets.

3. As a result, a force is exerted on the coil.

  • Remember, the direction of the force exerted on the wire depends on the direction of the current flowing through the wire. The current on one side of the coil is flowing in the opposite direction to the current on the other side,
  • You can use Fleming’s left-hand rule to determine the direction of the force exerted on the coil.

4. The magnetic field will produce an upward force on one side of the coil and a downward force on the other side. This causes the coil to rotate.

  • In the case of the diagram, the magnetic field exerts an upward force on the left side and a downward force on the right side. This leads to a clockwise rotation of the coil.

5. The coil will continue to rotate until it reaches a vertical position.

  • At this point, there will be an upward and downward force acting on the coil.

6. A split ring commutator changes the direction of current every 180°, which ensures that the torque continues in the same direction.

  • The split ring commutator provides a point of contact between the coils and the external circuit.
  • Carbon brushes mounted on either side of the commutator connect the rotating and stationary parts of the motor. This ensures that the coil does not tangle.

7. Although the different sides of the coil are in opposite locations after a half spin, the reversed current keeps the coil in rotation.