The field normal to the plane of a wire of `n` turns and radis `r` which carriers `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. `(3h^(2))/(2r^(2))`
B. `(2h^(2))/(3r^(2))`
C. `(3r^(2))/(3h^(2))`
D. `(2r^(2))/(3h^(2))`
