Four very long, current carrying wires in the same plane intersect to form a square `40.0 cm` on each side as shown in figure. Find the magnitude and direction of the current `I` so that the magnetic field at the centre of square is zero. Wires are insulated from each other.

Answer

A, B, D

Explanation

`10A` and `8A` current produce inward magnetic field. While `20 A` current produces outward magnetic field. Hence, current in fourth wire should be `(20-10-8)A`. or `2A` and it should produce inward magnetic field. So, it should be downwards tward the bottom.