Describe how an electric motor works, including how the forces on the coil cause it to rotate.

AQA GCSE Physics (8463) — 4.7.2 The motor effect · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

An electric motor contains a coil of current-carrying wire placed between two permanent magnets.

Model answer (4 marks)

1. The coil has two sides carrying current in opposite directions.
2. Each side experiences a force from the motor effect (interaction of the magnetic field and the current).
3. The forces on the two sides act in opposite directions.
4. The opposing forces make the coil rotate.

Examiner tips

Use the word ‘opposite’ to link the current directions and forces. Show the sequence: current → force → opposite forces → rotation. Keep each point short and to the point.

Common mistakes

Mixing up the direction of current on the two sides. Forgetting to mention that the forces are opposite. Using vague language like ‘pushes the coil’ instead of ‘forces act in opposite directions’.

Mark scheme (4 marks)

The two sides of the coil carry current in opposite directions (to each other)
Each side of the coil experiences a force due to the motor effect (interaction between the magnetic field and the current-carrying wire)
The forces on the two sides of the coil act in opposite directions
The opposing forces cause the coil to rotate

Key terms in this question

electric motor