Question

Magnetic field due to a toroid inside its turns is given by ($n$ is thenumber of turns per unit length of the toroid and $I$ is the current in the loop)

• A. $B={\mu }_{o}nI$
• B. $B={ϵ}_{o}nI$
• C. $B=\frac{{\mu }_o}{4\pi }nI$
• D. None of these

Answer 1

The correct option is A $B={\mu }_{o}nI$

Let the toroid be as above with a,r,b as internal radius, toroid radius and outer radius and current is I.

Now the magnetic field can be calculated by Ampere's law as below:

$B2\pi r=\mu NI$

Where B= magnetic field, N= number of turns

$⟹B=\frac{\mu NI}{2\pi r}$

$B=\mu nI$

where n= number of turns per metre length.