Date: Tue Mar 17 12:42:57 2009 Back to Contents ------------------------------------------------------------------------

Author: Sam Sampere

Subject: Re: Power Lines and compasses?


I have a demo where you plug a coil into 120 VAC, and a 100 W lamp in series with another coil lights up when the coils are brought near. I had a graduate student tell me that ALL my compasses were defective. None showed a deflection when brought near the coil. Silly grad student.

I wound a large multiturn coil around the projection screen in the auditorium. An amplifier driven by a function generator supplies 10+ amps through this coil. It's fun to watch the large demo compass turn slowly, i.e. 1 Hz.


-----Original Message-----
From: [] On Behalf Of Zani, Gerald
Sent: Tuesday, March 17, 2009 11:23 AM
Subject: Re: [tap-l] Power Lines and compasses?

I laid a hall probe onto an AC power cable attached to a 90 Watt lamp
and measured the B field. Nothing.

Then I wound the AC power cable into a few loops and measured with the
hall probe. Nothing.

Then I placed a compass on the same AC power cable for with a 90 Watt
lamp and looked for a deflection.


The article neglected to assume it was spherical cow...

- JZ

"To do nothing at all is the most difficult thing in the world, the most
difficult and the most intellectual." -- Oscar Wilde

On 3/17/09 6:42 AM, ""


> I just read an article in the newspaper this morning claiming that
> power lines affect cattle's sense of direction. The researchers say
> that generally cattle tend to line themselves up with the earth's
> magnetic field (which, along with our magnetic declination, may
> explain cow dipping in our neck of the woods ;-) but if they are near
> power lines they don't. My puzzlement is that the average magnetic
> field from a power line ought to be zero since they transmit AC power
> and they are strung in pairs. So I was wondering if any of you have
> experience with using compasses around power lines (or around cattle
> for that matter;).
> Cliff

From Tue Mar 17 12:42:57 2009