Question

What is a toroid? Mention an expression for magnetic field at a point inside a toroid?

Answer 1

A toroid is a coil of insulated or enamelled wire wound on a doughnut -shaped form made of powdered iron. A toroid is used as an inductor in electronic circuits, especially at low frequencies where comparatively large inductance are necessary.

Magnetic field due to toroid : -

$\oint \overrightarrow{B}.\overrightarrow{dl}={\mu }_0{I}_0$

$\oint \overrightarrow{B}.\overrightarrow{dl}$ = $\oint B.dlcos{0}^0$

$=B\oint dl=B\left(2\pi r\right)$

and ${\mu }_0{I}_0={\mu }_{0}n\left(2\pi r\right)I$

$\therefore B={\mu }_{o}nI$.

Thus magnetic field exists only in the tubular area bounded by the coil and it does not exist in the area inside and outside the toroid.