Case Study: The Azimuthal Magnetic Field in the Earth’s Core

Abstract

The magnetic field in the core of a rotating body such as the Earth, or the planets, or the Sun, or the stars, originates in electric currents that flow both in the core and in the atmosphere. So the source of the magnetic field rotates with the body. Does it make sense to apply the results of Chapter 8 here? That problem will require some thought. We must of course distinguish between a fixed reference frame S and a frame S′ that rotates with the body. But no! We have excluded rotating frames! So we have two problems: first, the source moves and, second, we must deal with rotation, and not with translation. As we shall see, the electric space charges in the rotating body play a crucial role.1