A uniformly charged disk like the disk in Fig. 21.26 has radius 2.50 cm and carries a total charge of 4.0 X 10-12 C.
(a) Find the electric field (magnitude and direction) on the x-axis at x = 20.0 cm.
(b) Show that for x » R, Eq. (21.11) becomes E = Q/4πє0x2. Where Q is the total charge on the disk.
(c) Is the magnitude of the electric field yon calculated in part (a) larger or smaller than the electric field 20.0 cm from a point charge that has the same total charge as this disk? In terms of the approximation used in part (b) to derive E = Q/4πє0x2 for a point charge from Eq. (21.11), explain why this is so.
(d) What is the percent difference between the electric fields produced by the finite disk and by a point charge with the same charge at x = 20.0 cm and at x = 10.0cm?