DC Electric Motor

A DC electric motor converts electrical energy into kinetic energy (rotation). It works because a current-carrying conductor in a magnetic field experiences a force (the motor effect).

How a simple DC motor works

1. A rectangular coil of wire is placed between the poles of a permanent magnet.
2. Current flows through the coil via carbon brushes that press against a split-ring commutator.
3. Each side of the coil experiences a force (Fleming’s left-hand rule). The forces on opposite sides act in opposite directions, creating a turning effect (couple).
4. When the coil reaches the vertical position, the commutator reverses the direction of current in the coil. This ensures the forces continue to push the coil in the same rotational direction.
5. The coil continues to rotate.

The commutator

The split-ring commutator is essential. Without it, the coil would rotate to the vertical position and stop (or oscillate back and forth). The commutator reverses the current direction every half-turn, keeping the rotation continuous.

Increasing the speed or force

The motor spins faster or with greater force if you:

• Increase the current
• Use a stronger magnet
• Increase the number of turns on the coil
• Place a soft iron core inside the coil (concentrates the magnetic field)

Reversing the direction

The motor reverses direction if you either:

• Reverse the current (swap the battery connections), OR
• Reverse the magnetic field (swap the magnet poles)

Doing both at the same time keeps the original direction.