Question

The ends of a circular coil of radius $r$ and number of turns $n$ is connected to the two terminals of a cell. The magnetic field at the centre of the coil is $B$. If the number of turns be made $2n$ keeping the radius same, the magnetic field at the centre of the coil will be:

• A. $B$
• B. $2B$
• C. $3B$
• D. $4B$

Answer 1

The correct option is B $2B$

$\left|B\right|=\frac{n{\mu }_{0}i}{2r}$
From this relation we can directly say that
$B\propto n$

So by doubling the number of turns, double will be the magnetic field.