Question

A current passing through a circle coil of two turns produces a magnetic field $B$ as its centre. The coil is then rewound so as to have four turns and the same current is passed through it. The magnetic field at its centre now is

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

Answer 1

The correct option is A $2B$

Magnetic field at the center of circular coil is given as:

$B=\frac{{\mu }_{0}nI}{2R}$

where $n$ is the number of turns there are in the coil.

Thus $\frac{B^{\prime }}{B}=\frac{n^{\prime }}{n}=\frac{4}{2}=2$

$⟹B^{\prime }=2B$