Question

A toroid with mean radius of 20 cm & 490 turns is filled with powder steel (having magnetic susceptibility 999). If 4.0 A current flows in toroid windings, then find the value of $B$ inside the toroid ?

• A. 3 mT
• B. 4 mT
• C. 1 mT
• D. 2 mT

Answer 1

The correct option is D 2 mT

$B={\mu }_0\left(\frac{N}{2\pi r}\right)i$
$B$= $4\pi \times {10}^{-7}\times \frac{490}{2\pi \times 0.2}\times 4$
$=\frac{4\pi \times {10}^{-7}\times 4900\times 4}{4\pi }$
$=4900\times 4\times {10}^{-7}$
$=1.96\times {10}^{-3}$
$\simeq$ 2 mT