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

["John Clement" <clement@hal-pc.org>]

It looks like a good demo.  And I hope you ask them to predict what they
might see and which pole of the magnet is producing the effect.  I use the
Minds on Physics demo where they have a bar magnet hung in a paper sling on
a thread from a wooden stand.  Actually I set several of them up ahead of
time and give them bar magnets.  They quickly realize that the N end of the
magnet points to the N compass direction.  I had a complete reference frame
X, Y, Z in my room with the ends labeled N, S, E... As well as X, Y, Z and
the appropriate signs.  It has dm ticks with labels each m.

I still would like to see the original questions.  Perhaps a colleague wrote
them down.

John 



> 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!
> _______________________________________________
> Forum for Physics Educators
> Phys-l@mail.phys-l.org
> http://www.phys-l.org/mailman/listinfo/phys-l