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 2-direction 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 distances outside the toroid.
D. is pointing radially outwards.

Answer

C

Explanation

As we know that a toroid can be considered as a ring shaped closed solenoid. So that it is like an endless cylindrical solenoid .

So, the magnetic field is only confined inside the body of a toroid in the form of concentric magnetid lines of force.
For any point inside, the empty space surrounded by toroid and outside the toroid.
the magnetic field B is zero because the net current, enclosed in , thense spae is zero. So that the magnetic moment of toroid is zero. In general, if we taker as a long distance outside the toroid the`m prop (1)/(r ^(3))` but this case is not possible here