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Re: [Phys-L] problems with the physics regents



I do a silly little demonstration that always gets a more enthusiastic response than I expect:

1. First, cover a bar magnet with a piece of newsprint and sprinkle iron filings. Tap the paper to shake the filings so that they line up with the field lines.

(Already, my 11th graders are stunned. Actually, so am I. They are stunned by the phenomenon which they swear they have never seen and I am stunned that they did not see this in elementary school...)

2. Now take one of those clear compasses used on overhead projectors and move it around to different points over the filings. Of course, the compass lines up with the "local" magnetic field lines.

3. Now pretend you are an explorer, following your compass to the "North" pole. You would just go the way it directed you. So I slowly move my compass over the filings, always moving in the direction that the compass calls "North". As expected, no matter where I start, I eventually "arrive" at one end of the bar magnet.

4. Remove the newspaper to reveal that the end of the bar magnet we have reached is actually the one with an S on it!

Moral of the story: while the Earth's magnetic field is NOT caused by a giant buried bar magnet...if it WERE, the pole found in the northern hemisphere would have a great big S on it!