GCSE Physics · Edexcel 1PH0 · Topic 12C
The motor effect
Key points
- The motor effect: a wire carrying a current at right angles to a magnetic field feels a force.
- Size of force: , where is magnetic flux density in tesla (T), is current and is length of wire in the field.
- The force is greatest when the wire is at right angles to the field and zero when parallel.
- Fleming's left-hand rule: First finger = Field, seCond finger = Current, thuMb = Motion (force).
- In a d.c. motor, forces on opposite sides of a coil act in opposite directions, making it turn. A split-ring commutator reverses the current every half turn to keep it rotating.
- Motor speed increases with larger current, stronger magnets or more turns on the coil. Loudspeakers also use the motor effect.
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Put a current-carrying wire in a magnetic field and it feels a force. This motor effect is how electric motors, fans, drills and loudspeakers turn electrical energy into movement.
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