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Electricity and Magnetism

Measuring the Strength of a Magnetic Field

When current flows through a conductor which is in a magnetic field, the conductor experiences a force (unless the current flows parallel to the magnetic field).

The direction of the force is at 90° to both the current and the magnetic field.

Fleming’s left hand rule helps to remember the relation between the three directions.


Factors affecting the Magnitude of the force

Experiments show that:

F SYGMA the current, I
F SYGMA the length of conductor in the field,
Therefore, F = (a constant).I.

and, if the current flows at 90° to the field, the constant is called the magnetic flux density (symbol, B).

B is a measure of the strength of the magnetic field.

units of B are NA-1m-1 or Teslas (T)

Flux density is the force per unit current per unit length acting on a conductor placed at 90° to the field.

If the conductor is placed at an angle OMEGABSM to the field, then the force is given by:

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