A conducting circular loop of radius a is connected to two long, straight wires. The straight wires carry a current i as shown in figure. Find the magnetic field B at the centre of the loop.

Question

G1 Physics · Accepted Answer

At the centre, the straight radial portions give zero because dℓ is parallel to the position vector. The two semicircular parts of the loop carry current in opposite senses and produce equal and opposite fields. Therefore the net field is zero, so A.