# Sphere of magnetic material in an applied field

1. May 14, 2009

### dave4000

1. The problem statement, all variables and given/known data

Consider a sphere of magnetic material with radius R and magnetisation M in an applied field $$B_{applied}$$. Find an expression for:

a) the total current flowing around the surface of the sphere;
b) the net field at the centre of the sphere.

2. Relevant equations

3. The attempt at a solution

I am totally new to the magnetisation physics, and am having trouble getting to grips with it, any pointers on how to go about solving this?

Last edited by a moderator: Apr 24, 2017
2. May 19, 2009

### dave4000

$$I=\int J.dS = \int (\nabla \times M).dS = 4\pi R^{2}M$$

Is this correct without $$B_{applied}$$? If so, what happens when $$B_{applied}$$ is present?