# Vector B in Magnetic Potential Energy

1. May 14, 2013

### Phztastic

U = -m x B

Is B the total magnetic field of the whole system?
If there is two objects X,Z and they all have a magnetic field. But different strengths,
I want to calculate the U for Z, B should be the total magnetic field of BOTH fields or only X's field strength?

Since X is the external magnetic field.

2. May 15, 2013

### Wiz700

In the calculation of U = -m x B
You should only take account of the EXTERNAL MAGNETIC FIELD acting on the magnetic moment.
Meaning, if you'd like to figure out the U of Z, then only use the magnetic field of X.

Similarly if you want to calculate U of X, then you use only the magnetic field of Z.

I wonder, is the potential energy of both X and Z the same, I'll leave that up to you Phztastic.

3. May 16, 2013

### Meir Achuz

$U=-m\cdot B$ if U is the energy, m is a permanent magnet, and B is the external field.