# Magnetic Field at the center of a sphere magnet

1. Apr 19, 2013

### hansbahia

1. The problem statement, all variables and given/known data
A sphere magnet of radius a has permanent uniform magnetization, z-axis. So we were trying to find the magnetic field at the center of the magnet in class.

2. Relevant equations
$j_M(θ)=Msin(θ)$

$dI=j_M(θ)adθ$

circular loop

$r_{loop}=asin(θ)$

3. The attempt at a solution

When using Biot-Savart equation for magnetic field of a ring why do you use*
$R^3=(a^2+z^2)$

$R^3=(r_{loop}^2+z^2)$

for the denominator????

Last edited: Apr 19, 2013
2. Apr 19, 2013

### TSny

Did you mean to write R2 instead of R3?

Can you show that the effective current due to the magnetization is zero everywhere except at the surface of the sphere?