A toroid has a core (non-ferromagnetic) of inner radius 25 cm and outer radius 26 cm,

Solution:

Inner radius of the toroid, r1 = 25 cm = 0.25 m

Outer radius of the toroid, r2 = 26 cm = 0.26 m

Number of turns on the coil, N = 3500

Current in the coil, I = 11 A

(a) Magnetic field outside a toroid is zero. It is non-zero only inside the core of a toroid.

(b) Magnetic field inside the core of a toroid is given by the relation,

$B=\frac{\mu_{0} N I}{l}$

Where,

$\mu_{0}=$ Permeability of free space $=4 \pi \times 10^{-7} \mathrm{~T} \mathrm{~m} \mathrm{~A}^{-1}$

$I=$ length of toroid

$=2 \pi\left[\frac{r_{1}+r_{2}}{2}\right]$

$=\pi(0.25+0.26)$

$=0.51 \pi$

$\therefore B=\frac{4 \pi \times 10^{-7} \times 3500 \times 11}{0.51 \pi}$

$\approx 3.0 \times 10^{-2} \mathrm{~T}$

(c) Magnetic field in the empty space surrounded by the toroid is zero.