The Motor Effect

This lesson explains the motor effect — the force experienced by a current-carrying conductor placed in a magnetic field — and how to use Fleming's left-hand rule to predict the direction of the force, as required by the Edexcel GCSE Combined Science specification (1SC0).

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What Is the Motor Effect?

When a current-carrying conductor (e.g. a wire) is placed in a magnetic field, it experiences a force. This is called the motor effect.

The force arises because the wire's own magnetic field (due to the current) interacts with the external magnetic field, producing a resultant force on the wire.

Conditions for a Force

A force is produced only if:

1. The wire carries a current, AND
2. The wire is in an external magnetic field, AND
3. The wire is not parallel to the field lines (the force is greatest when the wire is perpendicular to the field).

If the wire is parallel to the field lines, there is no force.

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Fleming's Left-Hand Rule

Fleming's left-hand rule gives the direction of the force on the conductor.

Hold your left hand so that: