Question:
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 an x-y plane. Its magnetic moment m
(a) is non-zero and points in the z-direction by symmetry
(b) points along the axis of the toroid
$m=m \hat{\phi}$
(c) is zero, otherwise, there would be a field falling as 1/r3 at large distances outside the toroid
(d) is pointing radially outwards
Solution:
(c) is zero, otherwise, there would be a field falling as 1/r3 at large distances outside the toroid