Solution: To calculate the current, an infinitesimal ring is “cut” out of the disk and viewed as a loop. Now, we can calculate
the emf induced in this ring and its resistance. From these, we obtain the power dissipated in the infinitesimal ring. To find
the total power dissipated in the disk, we integrate the power over all rings that make up the disk:
(a) Consider Figure 10.19b. The total flux enclosed in the ring of radius r is