Q. If in a circular coil $A$ of radius $R,$ current $i$ is flowing and in another coil $B$ of radius $2R$ a current $2i$ is flowing, then the ratio of the magnetic fields, $B_{A}\ and\ B_{B}$ produced by them will be
A) 1
B) 2
C) $\frac{1}{2}$
D) 4
Explanation
(a) Magnetic field in circular coil $A$ is
Similarly, $B_{A} = \frac{\mu_{0}Ni}{2R}$
$R$ is radius and $i$ is current flowing in coil.
$B_{B} = \frac{\mu_{0}N(2i)}{2\ .(2R)}$
$\ \ \ \ \ \ \ = \frac{\mu_{0}Ni}{2R}$
$\frac{B_{A}}{B_{B}} = \frac{1}{1} = 1$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.