Q. Magnetic field due to a ring having $n$ turns at a distance $x$ on its axis is proportional to (if $r =$ radius of ring)
A) $\frac{r}{(x^{2} + r^{2})}$
B) $\frac{r^{2}}{\left( x^{2} + r^{2} \right)^{3/2}}$
C) $\frac{nr^{2}}{\left( x^{2} + r^{2} \right)^{3/2}}$
D) $\frac{n^{2}r^{2}}{\left( x^{2} + r^{2} \right)^{3/2}}$
Explanation
(c) Magnetic field on the axis of circular current
$B = \frac{\mu_{0}}{4\pi}.\frac{2\pi nir^{2}}{\left( x^{2} + r^{2} \right)^{3/2}} \Rightarrow B \propto \frac{nr^{2}}{\left( x^{2} + r^{2} \right)^{3/2}}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.