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. is non-zero and points in the z-direction by symmetry
B. points along the axis of the toroid `(vecM=Mhatphi)`
C. is zero, otherwise there would be a field falling as `1/r^3` at large distance outside the toroid
D. is pointing radially outwards.

Answer

C

Explanation

In case of a toroid, the magnetic field is only confined inside the body of toroid in the form of concentric magnetic lines of force and there is no magnetic field outside the body of toroid. Thus the magnetic moment of toroid is zero. Hence, option (c) is correct.