4.

(a) An infinitely long solid conductor of radius a is placed along the z-axis. If the con-

ductor carries current / in the +z direction, show that

I

H

Ip

2πa²

a

within the conductor. Find the corresponding current density.

(b) If I = 3 A and a = 2 cm in part (a), find H at (0, 1 cm, 0) and (0,4 cm, 0).