Force on a current-carrying conductor

A current-carrying conductor (i.e. any wire within a complete circuit) experiences a force when placed in a magnetic field due to its own magnetism. This is called the motor effect.

We use Fleming's left hand rule to find out the correct direction of force.


Key Concepts

Fleming's left hand rule

Fleming's left hand rule reminds us that the magnetic field direction, conventional current direction and force produced must be perpendicular. It can be used for working out the direction of the force on a current-carrying conductor in a magnetic field.

Flux density

Flux density is the magnetic equivalent of field strength, but is defined in terms of the force on a conductor not the force on a magnet.

Definition of the ampere

The ampere (A) is the fundamental unit of current in electricity. It is defined in terms of the force between two parallel wires.

Essentials

Rotating coil

If a coil of wire has an axle running through it to enable rotation, and the coil of wire is in a plane parallel to the magnetic field, then you will have the basis of a continuous electric motor.

The force on each side is in the opposite direction so the coil rotates.

Non-perpendicular fields

An exam question will not necessarily always have the magnetic field perfectly at right angles to the current. In these cases, use \(\sin \theta\) to find the component that is.

Test Yourself

Use quizzes to practise application of theory.


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Exam-style Questions

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