Mail Archives: geda-user/2012/03/16/10:35:22

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Date: Fri, 16 Mar 2012 07:35:03 -0700
From: Joe Knapp <joeknapp AT keensupport DOT net>
Organization: Keen Support Services, LLC
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To: geda-user AT delorie DOT com
CC: Rob Butts <r DOT butts2 AT gmail DOT com>
Subject: Re: [geda-user] Daughter's Science Fair
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Reply-To: geda-user AT delorie DOT com


You mention parallel and adjacent and that go me thinking about my
motors and transformers classes. I think what you may need to acquaint
yourself with is the concept of magnetic flux density.

Here is a good illustration of you electromagnet:

The blues lines represent the lines of magnetic flux, the denser the
lines the stronger the magnetic force. You may notice that only two
lines are drawn as circles, actually all the flux lines make circles,
but illustrating them would make the illustration look like a toroid and
less clear. None the less, you can see that the magnetic forces are
concentrated in the center (i.e. in your nail) and expand when they
leave your coil and reconnect with the opposite polarity.

Finally, the flux density is highest at the end of your nail and not the

Good Luck,


On 03/16/2012 07:02 AM, Rob Butts wrote:
> My nine-year-old daughter has a science fair tomorrow.  We are doing
> simple electromagnets out of nails.  We are just using one C battery
> with approximately a 30-penny nail and 26 guage wire wrapped around
> the nail for two layers.  When the battery is connected the nail has a
> good magnetic strength in that it will pick up another nail not just
> paper clips.
> I was thinking about showing how a current in one coil will induce a
> current in another (how an electric toothbrush charges).  We rigged up
> another nail the same way but with a little bulb attached.  Check my
> theory, shouldn't the electromagnetic field produced by the coil and
> nail with the battery induce a current in the other coil when placing
> the nails adjacent and parallel?

Keen Support Services, LLC

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