A toroid has a core (non-ferromagnetic) of inner radius 25 cm and outer radius 26 cm, around which 3500 turns of a wire are wound. If the current in the wire is 11 A, what is the magnetic field (a) outside the toroid, (b) inside the core of the toroid, and (c) in the empty space surrounded by the toroid.

Explanation

B for a toroid is given by the same formula as for a solenoid: `B = mu_0 nI`, where n in this case is given by `n = (N)/(2pi r)` . The field is non-zero only inside the core surrounded by the windings. (a) Zero, (b) `3.0 x× 10^(-2)` T, (c) zero. Note, the field varies slightly across the cross-section of the toroid as r varies from the inner to outer radius. Answer (b) corresponds to the mean radius r = 25.5 cm.