Current flows through a straight cylindrical conductor of radius r. The current is distributed uniformly over its cross-section. The magnetic field at a distance x from the axis of the conductor has magnitude B.
(a) B = 0 at the axis.
(b) B ∝ x for 0 ≤ x ≤ r.
(c) B ∝ 1/x for x > r.
(d) B is maximum for x = r.
