SSE JE Electrical Engineering 29 Oct 2020 Shift 2 Papers

At distance r from an infinitely long straight current carrying conductor, magnetic field is:
$\mathrm{B}=\frac{\mathrm{\mu }\mathrm{I}}{2\mathrm{\pi }\mathrm{r}}$
where B is the magnetic field, ${\mathrm{\mu }}_0$ permeability of the medium I is the current in the wire, and r is the distance from the wire to that point.
So $\mathrm{B}\propto \frac{1}{\mathrm{r}}$