Figure shows a square loop made from a uniform
wire. Find the magnetic field at the centre of the square
if a battery is connected between the points A and C.

Explanation

The current will be equally divided at A. The fields at the centre due
to the currents in the wires AB and DC will be equal in magnitude
and opposite in direction. The resultant of these two fields will be
zero. Similarly, the resultant of the fields due to the wires AD and
BC will be zero. Hence, the net field at the centre will be zero.