Magnetic dipole moment?

Question

The magnetic dipole moment of Earth is 7.00x10^22 J/T. Assume that this is produced by charges flowing in Earth's molten outer core. If the radius of their circular path is 3600 km, calculate the current they produce.

Answer 1

Assuming a planar current loop, magnetic dipole moment μ = Ia, where I is current and a is the loop area.

I = μ/a = 7E22/(2π*3.6E6^2) = 8.596E8 A