Question

Question 4.17: 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.

Class 12 - Physics - Moving Charges And Magnetism Moving Charges And Magnetism Page-170

Answer 1

total number of times in the toroid are given 3500.e.g., N = 3500
(a) outside the toroid, the magnetic field is zero.
(b) inside the core of toroid, the magnetic field will be $B=\mu_0nI$
here, n is the number of turns per unit length
and I is the current passing through toroid.
now, $B=\mu_0\frac{N}{2\pi r}I$
here, r can be taken as mean of inner and outer radius of toroid.
e.g., r = (26 + 25)/2 = 25.5 cm
so, B = (4π × 10^-7 × 3500 × 11)/(2π × 25.5 × 10^-2)
= 3 × 10^-2 T

(c) magnetic field in the empty space surrounded by the toroid is also zero. because current through it is zero.