Chapter 32, Problem 47P

SSM ILW WWW The magnitude of the magnetic dipole moment of Earth is 8.0 × 10²² J/T. (a) If the origin of this magnetism were a magnetized iron sphere at the center of Earth, what would he 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 × 10^–23 J/T. (Note: Earth’s inner core is in fact thought to he 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.)