Abstract
The geodynamo usually appears as a somewhat intimidating subject. Its understanding seems to require knowledge of the intricate theory of magnetohydrodynamics. The solution of the corresponding equations can only be achieved numerically. It seems to be a subject for the specialist. We show that one can understand the basics of the functioning of the geodynamo solely by using the well-known laws of electrodynamics. The topic is not only important for geophysicists. The same physics is the cause for the magnetic fields of Sun-like stars, of the very strong fields of neutron stars, and also of the cosmic magnetic fields.
Highlights
In the physics lecture, the origin of the magnetic field of the Earth is usually only briefly mentioned
The students learn the following: The field does not originate from a permanent magnet, because the temperature inside the Earth is too high. It is caused by electric currents which are generated in the same way as with a self-excited dynamo: by the movement of an electrical conductor in a magnetic field
The self-excited dynamo has some characteristics that we find in the geodynamo, and which we would like to highlight here
Summary
The origin of the magnetic field of the Earth is usually only briefly mentioned. The students learn the following: The field does not originate from a permanent magnet, because the temperature inside the Earth is too high It is caused by electric currents which are generated in the same way as with a self-excited dynamo: by the movement of an electrical conductor in a magnetic field. This “geodynamo” is driven by the thermal convection of the liquid iron inside the Earth. This movement within the magnetic field results in an electric current j1, Figure 4b. This contribution is important for an understanding of the geodynamo because we see that the initial field B0 is no longer needed
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