A long straight wire of radius R carries a current distributed uniformly over its cross-section. Then
I. The magnitude of the magnetic field is minimum at the axis and maximum of the surface of the wire
II. The magnetic field at a distance x from the axis of conductor $B\alpha x$ for  $0\le x\le R$  and $B\alpha \frac{1}{x}$ for   x > R.
III. The $Bv/sx$ graph is