An insulating sphere is 20 cm in diameter, and carries a +4.2 µC charge uniformly distributed throughout its interior volume. Calculate the charge enclosed by a concentric spherical surface with the following radii:
(a) r = 5 cm,
(b) r = 10 cm
(c) r = 15 cm.
During fair weather, an electric field of about 100 N/C points vertically downward into the earth's atmosphere. Assuming that this field arises from charge distributed in a spherically symmetric manner over the surface of the earth, determine the net charge of the earth and its atmosphere if the radius of the earth and its atmosphere is 6.37 x 106 m.