Question

magnetic field B on the axis of a circular coil far away at distance X from the centre of the cell are related as

Answer 1

The formula for the magnetic field B (flux density) at P at a distance d from the center of O the coil on the axis of the coil of radius r :

$B(distance\ X)=\frac{\mu_0}{2} \frac{i*r^2}{(r^2+X^2)^{\frac{3}{2}}}\\\\X \ \textgreater \ \ \textgreater \ radius\ r\\\\B=\frac{\mu_0}{2} \frac{i*r^2}{X^3}$