Moving Charges And Magnetism

A circular coil of radius '\(r\)' and number of turns ' $n$ ' carries a current '\(I\)'. The magnetic fields at a small distance '\(h\)' along the axis of the coil \(\left(B_a\right)\) and at the centre of the coil \(\left(\mathrm{B}_{\mathrm{c}}\right)\) are measured. The relation between \(B_c\) and \(B_a\) is