The magnitude of the magnetic dipole moment of Earth is 8.0 x 1022 J/T.

(a) If the origin of this magnetism were a magnetized iron sphere at the center of Earth, what would be its radius?

(b) What fraction of the volume of Earth would such a sphere occupy? Assume complete alignment of the dipoles. The density of Earth's inner core is 14 g/cm3.The magnetic dipole moment of an iron atom is 2.1 x 1023 J/T.(Note: Earth's inner core is in fact thought to be in both liquid and solid forms and partly iron, but a permanent magnet as the source of Earth's magnetism has been ruled out by several considerations. For one, the temperature is certainly above the Curie point.