The Biot – Savart Law makes it possible to find the magnetic field at each point in space due to a distribution of electric currents. The Law is completely general and can in principle be used whatever the distribution of currents. In many situations however, the problem has symmetry which makes much simplification possible. For the example of the magnetic field on the axis of a current loop, all the components of the magnetic field directed off the axis of the loop cancel out and the net magnetic field on the axis is directed along the axis – this result is due to the circular symmetry of the loop.
The Biot – Savart Law states
where
is a tiny piece of current loop and hat r is the unit vector in the direction of
For the point on the axis of the current loop above
and
Hence 
When
at the centre of the coil,