# B How is the strength of a magnetic field measured?

1. Jul 13, 2016

### TheAnt

I was wondering at what point the strength of the magnetic of a magnet was mea. I assume it would not be the origin of the field which would be inside the magnet and not the side of the magnet itself as the value would be dependant of the size of the magnet.
Is there a standard of where to measure the field eg. 1 m away from the ce ter of the magnet?
Thank you

2. Jul 13, 2016

### CWatters

My understanding is that permanent magnets are measured in a machine that effectively has a "keeper" between the poles. The flux in the "keeper" is the specified "strength" of the magnet. It's the maximum magnetic flux the magnet can produce. When the "keeper" is removed the flux is free to spread out, essentially becoming less concentrated. So if you try to measure the flux in the air at some distance from a pole you will get a lower value.

I found..

http://www.first4magnets.com/tech-c.../how-is-the-strength-of-a-magnet-measured-i81

Selected extracts...

3. Jul 19, 2016

### gre_abandon

You can measure magnetic field through Hall effect. Suppose you have a piece of conductor of square shape with the four edges labeled A,B,C,D. If you apply a voltage across A,C there be a current. Now if you place this piece of material into magnetic field which will cause the charges in the material to deflect, there will be a voltage across B,D. By measuring the voltage across B,D one knows the strength of the magnetic field.