The Earth has a magnetic dipole moment of . We have to estimate the current that would have to be set up in a single turn of wire going around the Earth at its magnetic equator to set up such a dipole.

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The mean radius of the Earth,

.

Let the current that would have to be set up in a single turn of wire going around the Earth at its magnetic equator to set up a magnetic dipole moment of be .

We thus have the relation