Q. A circular coil of radius $R$ carries an electric current. The magnetic field due to the coil at a point on the axis of the coil located at a distance $r$ from the centre of the coil, such that $r > > R$, varies as
A) $\frac{1}{r}$
B) $\frac{1}{r^{3/2}}$
C) $\frac{1}{r^{2}}$
D) $\frac{1}{r^{3}}$
Explanation
(d) $B = \frac{\mu_{o}}{4\pi}.\frac{2\pi NiR^{2}}{r^{3}} \Rightarrow B \propto \frac{1}{r^{3}}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.