A circular loop of radius a, carrying a current I, is placed in a tow dimensional magnetic field. The centre of the loop coincides with the centre of the filed The strenght of the magnetic field at the pariphery of the loop is B. find the magnetic force on the wire.

Options

A. `2pi B i a`
B. `4pi B i a`
C. `pi B i a`
D. `B i a`

Answer

A

Explanation

Here direction of magnetic field is different at every point i.e. magnetic field is non-uniform. Consider a small length `dl`.
`dF = B i d l`
`F = Bi int dl = Bi. 2pi a = 2pi Bia`