GCSE Physics · AQA 8463 · Topic 4.7.2
The motor effect
Key points
- The motor effect: a wire carrying a current in a magnetic field experiences a force, because its own field interacts with the magnet's field.
- Fleming's left-hand rule: First finger = Field, seCond finger = Current, thuMb = Motion (force).
- (Higher tier) Force on a wire at right angles to the field: , where is magnetic flux density in tesla (T), is current in A and is length in m.
- An electric motor uses a coil in a magnetic field: forces on opposite sides act in opposite directions, so the coil rotates. A split-ring commutator reverses the current every half turn to keep it spinning.
- (Separate physics) Loudspeakers and headphones use the motor effect: an alternating current makes a coil and cone vibrate, producing sound.
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A current in a wire creates a magnetic field, and a wire carrying a current inside another magnetic field feels a force. The first idea gives electromagnets; the second, the motor effect, turns electrical energy into movement in every…
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