Question

By making different choices for the Amperian loop, show that B = 0 for poirits outside an ideal toroid.

Answer 1

From figure the inner Ampe'rean loop does not enclose any current while the outer Amperean loop encloses equal number of `I_"in"` and `I_"out"` Hence, by Ampere’s law, B = 0 outside an ideal toroid.