# Homework Help: Finding the current given a magnetic dipole, its plug in chug, whats going wrong?

1. Nov 2, 2005

### 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.

Last edited: Nov 2, 2005
2. Nov 3, 2005

### Galileo

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

3. Nov 3, 2005

### mr_coffee

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

4. Nov 3, 2005

### cepheid

Staff Emeritus
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.

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