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The Motor Effect

When a wire carrying an electric current is placed in a magnetic field, it may experience a force (The force is at a maximum when the current is flowing at right angles to the field lines and is zero when it is parallel to them.).

The size of the force can be increased by:

  • increasing the strength of the magnetic field it experiences;
  • increasing the size of the current flowing through it.
  • increasing the number of turns of wire experiencing the magnetic field.
     

The direction of the force is reversed if either the direction of the current or the direction of the magnetic field is reversed. It can be found using Fleming's Left Hand Motor Rule. (You can remember that it is the left had by remembering that in Britain we drive motor cars on the left hand side of the road - or by remembering that the motor rule predicts the direction of a resulting Force and LEFhas an F in it).

 

See Also:

 

For the AQA GCSE you should be able to use diagrams and/or other appropriate information to explain how electromagnetic effects are used in simple d.c. motors and circuit breakers.

NB Details of the split ring commutator, for reversing the current to a d.c. motor each half turn, will not be examined.

Here is an interesting demonstration that you could try at home!