Question

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. $\frac{1}{r^3}$

Answer 1

The correct option is D $\frac{1}{r^3}$

When $r>>R$, magnetic filed at a point on the axis of the loop :$B=\frac{{\mu }_0}{2\pi }\left(\frac{AI}{r^3}\right)$

$⟹B\alpha \frac{1}{r^3}$