A coil in the shape of an equilateral triangle of side l is suspended between the pole pieces of a permanent magnet such that \[\vec{B}\] is in plane of the coil. If due to a current i in the triangle a torque \[\tau \] acts on it, the side l of the triangle is

• A. \[\frac{2}{\sqrt{3}}{{\left( \frac{\tau }{B.i} \right)}^{\frac{1}{2}}}\]
• B. \[2{{\left( \frac{\tau }{\sqrt{3}B.i} \right)}^{\frac{1}{2}}}\]
• C. \[\frac{2}{\sqrt{3}}\left( \frac{\tau }{B.i} \right)\]
• D. \[\frac{1}{\sqrt{3}}\frac{\tau }{B.i}\]