Electric motors (HT only) — AQA GCSE Physics
Test yourself on Electric motors (HT only) with AQA GCSE practice questions.
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Electric motors (HT only) explained
A practical direct current motor turns that idea into hardware: a coil on an axle between the poles of a permanent magnet, fed through a split-ring commutator and two carbon brushes.
Read the full explanation
Without the commutator the coil would swing round to the vertical and stop, because beyond that point the same forces would push it back again. The split ring swaps the two ends of the coil over every half turn, so the current in whichever side is now on the left always runs the same way, the force on that side always points the same way, and the coil keeps turning in one sense. Making the current larger, using a stronger magnet, or winding on more turns all increase the turning effect. Reversing the current, or swapping the magnetic poles over, reverses the rotation, but doing both together changes nothing.
Your focus
- Name the parts of a direct current motor and state the job each one does.
- Explain why a motor built with a slip ring instead of a split ring would come to rest after half a turn.
- Predict the effect on a motor of reversing the current, swapping the magnetic poles, or doing both at once.
Show all 4 objectives
- Suggest three changes that would make a given motor turn faster and justify each one.
Electric motors (HT only) exam tips
Marking Points
- one mark for a coil carrying a current in the field of a permanent magnet
- one mark for the split-ring commutator reversing the current in the coil every half turn
- one mark for explaining that this keeps the force on each side acting the same way, so rotation continues
- one mark for a named way of increasing the speed, such as a larger current, more turns or a stronger magnet
Examiner Tips
- 💡Learn the parts list, coil, permanent magnet, split-ring commutator and brushes, and name them in any explanation.
- 💡If asked how to make the motor turn faster, change one thing at a time and say why it increases the force.
- 💡A question asking why the coil does not stop is always about the commutator; say what it swaps and how often.
Common Mistakes
- describing a slip ring rather than a split ring, which would let the coil come to rest after half a turn
- saying the commutator reverses the magnetic field, when it reverses the current in the coil
- reversing both the current and the magnets and then predicting reversed rotation, when the two changes cancel
- calling the coil an electromagnet that is attracted to the magnet, instead of using the motor effect force