A coil in the shape of an equilateral triangle of side 115 suspended between the pole pieces of a permanent magnet such that $\mathrm{B}^{-}$ is in plane of the coil. If due to a current $\mathrm{I}$ in the triangle a torque $\tau$ acts on it, the side 1 of the triangle is
(a) $(2 / \sqrt{3})(\tau / \mathrm{BI})^{1 / 2}$
(b) $(2 / 3)(\tau / B I)$
(c) $2[\tau /\{\sqrt{(} 3) \mathrm{BI}\}]^{1 / 2}$
(d) $(1 / \sqrt{3})(\tau / \mathrm{BI})$