A nonconducting disk has a radius R, carries a uniform surface
charge density s, and rotates with angular speed w.
(a) Consider an annular strip that has radius ?, width ??, and
charge ??. Show that the
current produced by this strip is ?? = ?????.
(b) Show that the net magnetic field at the center of the disk
is ?)???⁄2.
(c) Find the magnetic field on the axis of the disk, a distance
z from the center.