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 x-y plane. Its magnetic moment `vecM`
A. is non-zero and points in the Z-direaction by symmetry
B. points along the axis of the toroid `( m = m phi)`
C. is zero, otherwise there would be a field falling as `(1)/(r^(3))` at large distance outside the toriod
D. is pointing radially outwards

Answer 1

Correct Answer - C
In case of 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. This becasuet the loop encloses no current. Thus, the magnetic moment of toroid is zero. In general, if we take r as a large distance outside the toroid, then `alpha(1)/(r^(3))` . But this case is not possible here.