# Magnetic field measurements

1. Apr 3, 2008

### 7doughnuts

Hi

Can anyone tell me how magnetic field strength decreases with distance in free space? If the source was effectively a point souce in a plasma, what would the field strength be at a specific distance?

Is it source field strength/4 pi r sqrd?

As an example if the source was 1T, what would the measured field be at 5cm?

I've been reading some papers claiming massive field strengths inside dense plasmas and I'm curious as to how far these fields extend.

2. Apr 3, 2008

### rock.freak667

Well according to what I read somewhere

$$B=\mu H$$
Where H is field strength and B is flux density. But B would depend on what is being used to produce the magnetic field.

3. Apr 4, 2008

### Phlogistonian

The magnetic field of a moving charge falls off like 1/r^2.

However, we usually see magnetic fields in the form of dipoles. A dipole has a north and a south pole--like a bar magnet. The field of a dipole falls off like 1/r^3.

That's in free space. Inside a plasma, it gets more complicated, because plasmas conduct electricity and interact with magnetic fields in complex ways.