(ii) A solenoid bent into the form of closed loop is called toroid. The magnetic field B has a constant magnitude everywhere inside the toroid.
(a) Let magnetic field inside the toroid be B along the considered loop 1 as shown in the figure.
Applying Ampere’s circuital law,
(b) Magnetic field inside the open space interior of the toroid Let the loop 2 be shown in the figure, experience magnetic field B.
No current threads the loop 2 which lie in the open space inside the toroid.
By Ampere’s circuital law,
Magnetic field in the open space exterior of the toroid Let us consider a coplanar loop 3 in the open space of exterior of toroid. Here, each turn of toroid threads the loop two times in opposite directions.
Therefore, net current threading the loop = NI-NI = 0
By Ampere’s circuital law,
Thus, there is no magnetic field in the open space interior and exterior of the toroid.
