A toroid of n turns, mean radius R and cross-sectional radius a carries current I. It is placed on a horizontal table taken as x-y plane. Its magnetic moment `vecM`

Options

A. non-zero and points in the Z-direction by symmetry.
B. pointing along the axis of the toroid `(vecm = m vecpsi)`
C. zero, otherwise there would be a field falling as `(1)/(r^3)` at large distances outside the toroid.
D. pointing radially outwards.

Answer

C

Explanation

The magnetic field created by a toroid is limited to the area enclosed inside the coil. There is no magnetic field outside it. The magnetic moment of coil is perpendicular to the plane of coil. In case of toroid, all the coils are curved in such a manner that their magnetic moments form a closed loop so that the resultant is zero. So, the net magnetic moment is zero