Question

If we double the radius of a current carrying coil keeping the current unchanged, the magnetic field at its center:

• A. becomes four times.
• B. doubles.
• C. remains unchanged.
• D. is halved.

Answer 1

The correct option is D is halved.

For a coil carrying current, magnetic field at its center is given by:

$B=\frac{{\mu }_{o}I}{2R}$

i.e. $B\propto \frac{1}{R}$

On doubling the radius, magnetic field reduces to half.