# Difference in potential induced by a magnetostatic field? O_o

1. Sep 7, 2009

### Vectronix

Hi,

Why is there a difference in electric potential from a point on the surface of a stationary magnet to a point on a conductor that is placed underneath a dielectric? I placed some stationary magnets on top of glass or a piece of paper and put some aluminum under it, and touch one end of a voltmeter to the magnet and the other end of the voltmeter to the aluminum, the most I got was like 0.5 volts. When I remove the paper the potential difference is zero. If I remove the magnet, the potential difference is zero. When I have the magnet there at rest on top of the paper, which is above the aluminum, the potential difference is nonzero. When I start moving the magnet and the paper away from each other, the potential difference starts dropping quickly.

I thought that only a magnetic flux that is changing could induce a difference in potential. Anyone got an idea what's going on here?

2. Sep 12, 2009

### tiny-tim

Welcome to PF!

Hi Vectronix! Welcome to PF!
That's interesting … does anyone else know the answer?

(btw, does the potential difference reverse if you turn the magnet over? and does it work with other metals?)

3. Sep 12, 2009

### Bob S

Hi Vectronix-
This is a very good question, as is the suggestion by tiny-tim-
Are you talking about a dc potential, or a transient pulse (like discharging something). What is the input impedance of your voltmeter? If is something like 20 megohms. and the distributed capacitance is certainly less than a nanoFarad, then the transient would be less than RC = 0.02 seconds. You also told us that there is no dc circuit (loop), so there can be no current, or contact potential. So it is a puzzle.

By the way, do you happen to have an analog voltmeter with a D'Arsonval movement? See
http://www.engineersedge.com/instrumentation/electrical_meters_measurement/darsonval_movement.htm
Is it affected by stray magnetic fields?
Bob S

4. Sep 27, 2009

### Vectronix

Hey, muchachos. :)

I'm sorry, I have been busy for a while, and I wasn't able to get to this sooner. Yes, the potential difference reverses when I flip the magnet over. It is a DC potential, not a transient pulse. The voltage started off at a certain level then it decreased some and stabilized after a short while when I did this. Yes, it works with different metals. I tried aluminum and copper.

I was thinking that maybe the dielectric that I use (paper, glass, etc.) and probably every other dielectric and its electric fields influence the magnetostatic field of the magnets I use thus becoming a time-varying field (changing magnitude and/or direction). But I am not sure why, if that is true. Any thoughts on this explanation? Anything to add to it? I will answer the other questions soon.

5. Sep 28, 2009

### Bob S

Hi Vectronix-
Did you know that analog meters with D'Arsonval movements have moving magnets inside? Keep your magnets far away from these meters.
Bob S