A coil in the shape of an equilateral triangle of side l is suspended between the pole pieces of a r permanent magnet such that B is in place of the coil. If due to a current i in the triangle a torque ? acts on it, the side l of the triangle is-

Question

( A ) $\frac{2}{\sqrt3}[\frac{\tau}{Bi}]$
( B ) $\frac{2}{\sqrt3}[\frac{\tau}{Bi}]^\frac{1}{2}$
( C ) $2[\frac{\tau}{\sqrt{3}{Bi}}] ^\frac{1}{2}$
( D ) $\frac{1}{\sqrt3}\frac{\tau}{Bi}$