A wire is bent in the form of an equilateral triangle PQR of side 10 cm and carries a current of 5.0 A. It is placed in a magnetic field B of magnitude 2.0 T directed perpendicularly to the plane of the loop. Find the forces on the three sides of the triangle.

Explanation

Suppose the field and the current have directions as shows in figure. The force on PQ is `vecF_1 = I vec l xx vec B ` or `F_1 = 5.0 A xx 10 cm xx 2.0 T = 1.0 N.` The rule of vector product shows that the force `F_1` is perpendicular to PQ and is directed towards the inside of the triangle. The forces `vecF_1 , vecF_2, and vecF_3` will have zero resultant, so that there is no net magnetic force on the triangle. This result can be generalised. Any closed current loop, placed in a homogeneous magnetic field, dose not experience a net magnetic force.