Calculating Earth's Core Current: 6.2E8 A

[mr_coffee]

Hello everyone, I'm missing this problem and i aksed the professor if i was doing it wrong and he said, nope it looks like you just use that equation and solve for I. Here is the equation:
M = IA, where M stands for the moment; A stands for Area.
So you know the Moment is 1022 J/T. You also know the area is 4PIr^2;
A = 4PI(3200E3)^2;
A = 1.29E14;
I = M/A
I = (8E22)/1.29E14 = 620155038.8 = 6.2E8
Am i doing this right? It says its wrong!

The magnetic dipole moment of Earth is 8E22 J/T. Assume that this is produced by charges flowing in Earth's molten outer core. If the radius of their circular path is 3200 km, calculate the current they produce.

 

[Galileo]

The area enclosed by a circle is $\pi r^2$

 

[mr_coffee]

Ohh my bad, i thought the Earth was more of a sphere than a circle, thank you!

 

[cepheid]

Ohh my bad, i thought the Earth was more of a sphere than a circle, thank you!

Sure, the Earth is a sphere. But we're not talking about the Earth here! I think you need to take another look at the basic concept.

If the radius of their circular path is 3200 km...

We're talking about the area bounded by the circular path of the charges.