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 [EAMCET 1987; AIIMS 2004]

• A.            \[\frac{1}{r}\]
• B.            \[\frac{1}{{{r}^{3/2}}}\]
• C.            \[\frac{1}{{{r}^{2}}}\]       
• D.            \[\frac{1}{{{r}^{3}}}\]