Question

A coil in the shape of an equilateral triangle of side `l` is suspended between the pole pieces of permanent magnet. Such that `vecB` 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 triangel is:
A. `(2)/(sqrt(3))((tau)/(Bi))^((1)/(2))`
B. `(2)/(3)((tau)/(Bi))`
C. `2((tau)/(sqrt(3) Bi))^((1)/(2))`
D. `(1)/(sqrt(3)) (tau)/(Bi)`

Answer 1

Correct Answer - C
`tau = MB sin 90^(@) = MB`
`tau = iAB = i((sqrt(3) l^(2))/(4))B`
`l^(2) = (4 tau)/(sqrt(3)iB) rArr l = 2((tau)/(sqrt(3) Bi))^((1)/(2))`