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 $\overline{M}$.

• A. Is non-zero and points in the z-direction by symmetry
• B. Points along the axis of the toroid $(\overline{M}=M\hat{\varphi })$
• C. Is zero, otherwise there would be a field falling as $\frac{1}{r^3}$ at large distances outside the toroid
• D. Is pointing radially outwards

Answer 1

Answer: (C)

Is zero, otherwise there would be a field falling as $\frac{1}{r^3}$ at large distances outside the toroid

A toroid is a form of solenoid which is bend in the form of a circular coil. The magnetic field due to the toroid remains inside the circular coil of the toroid and it remains in the form of the concentric circles.

The magnetic field outside the toroid is zero and it varies as inversely proportional to the cube of the distance of the point.

Thus, option $\left(C\right)$ is correct.