Current `i` is carried in a wire of length `L`. If the wire is turned into a circular coil, the maximum magnitude of torque in a given magnetic field `B` will be

Options

A. `(LiB^(2))/(2)`
B. `(Li^(2) B)/(2)`
C. `(L^(2) iB)/(4pi)`
D. `(Li^(2) B)/(4pi)`

Answer

C

Explanation

`tau = iAB ` , as `r = (L)/(2pi)`
`= (ipi L^(2))/(4pi^(2)) ""B implies T_("max") = (iL^(2) B)/(4pi)`