The earth’s magnetic field, with a magnetic dipole moment of 8.0 × 10²² A m², is generated by currents within the molten iron of the earth’s outer core. Suppose we model the core current as a 3000-km-diameter current loop made from a 1000-km-diameter “wire.” The loop diameter is measured from the centers of this very fat wire.
a. What is the current in the current loop?
b. What is the current density J in the current loop?
c. To decide whether this is a large or a small current density, compare it to the current density of a 1.0 A current in a 1.0-mm-diameter wire.