Re: Appropriate for Gen Phys? was: comprehending electric/magnetic interactions

[John Clement <clement@HAL-PC.ORG>]

Unfortunately the science courses tell the students that a compass
needle is an example of a magnet rather than letting them hang a bar
magnet from a string and letting them see what happens.  One of the best
sets of magnet exploration labs has been published in Minds on Physics.
Students find out that the earth acts like a magnet by observing it.

Incidentally some other misconceptions involve the belief that students
have that magnets pick up metals.  Of course they are also given
aluminum and copper to play with.  In addition students will tell you
that magnets lose strength because the "magnetic particles" recombine or
they drop out when magnets are dropped.  These are often only revealed
when the students are given a test where they have to display
understanding of electrical forces, magnetic forces, and gravitational
forces.  Usually these topics are tested separately in HS so students
can easily memorize each one.  However when tested on all three the
problems are readily seen because they have to understand the
similarities and the differences between the 3 different models.  Then
of course there is the idea that the magnetic pole in Canada is really
the S pole of a magnet.

The common misconceptions about magnetic forces due to lack of good
exploration is similar to the problem with Pi.  Students do not
understand Pi because they have not done the simple things like wrapping
a string around various cans and comparing its length with the diameter.
Pi is generally treated as an abstract quantity in math courses and
students never even pick up a ruler or protractor in many math classes.

John M. Clement
Houston, TX


> I remember, in the sixth grade, considering a bar magnet held aloft
> by a helium balloon. I reasoned that only on the equator would the
> bar magnet not be able to 'decide' which way to drift.
>
> This followed from playing with a compass and bar magnet.
>
>         I am amazed (but no longer surprised) by the number of people
> who don't understand the relationship between a 'bar magnet' and a
> compass needle.
>
> At 3:35 PM -0400 7/3/03,  Robert Cohen wrote: