Question

A long wire is bent into a circular coil of one turn and then into a circular coil of smaller radius having $n$ turns. If the same current passes in both the cases, the ratio of magnetic fields produced at the centre for one turn to that of $n$ turns is

• A. $1 : n$
• B. $n : 1$
• C. $1 : n^2$
• D. $n^2 : 1$

Hint:

When a wire of fixed length is coiled into $n$ turns, the radius becomes $1/n$ of its original value, and the magnetic field at the center increases by a factor of $n^2$ because $B \propto \frac{n}{r}$.

Answer 1

The Correct Option is C