A conducting circular loop of radius r carries a constant current I. It is placed in a uniform magnetic field `vec(B)` such that `vec(B)` is perpendicular to the plane of the loop. The magnetic force acting on the loop is

Options

A. `irB_0`
B. `2piirB_0`
C. zero
D. `piirB_0`

Answer

C

Explanation

The magnetic field is perpendicular to the plane of the paper. Let us consider two diametrically opposite elements . By Fleming.s Left hand rule on element AB the direction of force will be Leftwards and the magnitude will be
`dF =IdlB sin 90^@ = IdlB`
On element CD, the direction of force will be towards right on the plane of the paper and the magnitude will be `dF=IdlB`.