Find out the expression for the magnetic field at a point on the axis of a toroid of N turns having average radius r and carrying a current I. Show that the magnetic field in the open space inside and outside the toroid is zero.

Explanation

2nd Part: If we take a closed loop in the open space inside a toroid (around its centre) or outside the toroid, the net current enclosed by the closed loop is zero. Hence the magnetic field there is zero.