The field normal to the plane of a wire of n turns and radius r which carries a current i is measured on the axis of the coil at a small distance h from the centre of the coil. This is smaller than the field at the centre by the fraction

• A.            \[\frac{3}{2}\frac{{{h}^{2}}}{{{r}^{2}}}\]
• B.            \[\frac{2}{3}\frac{{{h}^{2}}}{{{r}^{2}}}\]
• C.            \[\frac{3}{2}\frac{{{r}^{2}}}{{{h}^{2}}}\]
• D.            \[\frac{2}{3}\frac{{{r}^{2}}}{{{h}^{2}}}\]