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Re: teaching electric circuits

At 4:06 PM -0700 5/6/00, Leigh Palmer wrote:


>Perhaps this discussion belongs on PhysLerner (or whatever the
>pedagogical phys list is called) but I would encourage the nay-sayers
>on _THIS_ list to _TRY_ the suggested exercises with identical bulbs
>in various series/parallel combinations.

Where are the suggested exercises?

I just performed my demonstration (with matched 60 W bulbs) for a
meeting of the BC Section of the AAPT and put in a plug for phys-l.
I used it to illustrate the apparent conflicts introduced by this
complicating factor when the goal is to teach the applications of
Ohm's law. Try my demo, Chuck, and I'll try yours.

Leigh


I have been using a VERY effective lab for the past four years that
consists of 'Puzzle Boxes'.
Each box contains five (5) equivalent 120 volt Solstice Light Bulbs.
(Bought on sale each year after the annual Winter Solstice
celebration). Each string of lights provides the sockets AND
identical bulbs for mere pennies/bulb.

Each set of five bulbs is wired (reversibly, with 'wire nuts') inside
a flatish cardboard box. I'm now mounting them in VHS cassette boxes.
The arrangements of series and parallel bulbs is chosen to be fairly
random. Each bulb should glow at least dimmly when the contraption is
plugged into 120vac.

The student 'explores' the circuit within the box by loosening
various bulbs in their sockets. (They DON'T completely remove the
bulbs, because they could then stick various body parts into the
'live' sockets, and this would not be good!)

High school students have NO difficulty in DISCOVERING what is meant
by series and parallel circuits by using these boxes and absolutely
NO instruction from the 'Authority Figure' at the front of the class.

When two parallel bulbs are in series with a single bulb, the single
bulb is clearly brighter than the two that are in parallel with each
other and in series with the one. They say that the 'current' is
twice as big in the one since it has divided between the two in
parallel.

We do not intend to make luminosity measurements of these bulbs but
the students can clearly 'conceptualize' the lower current through
the dimmer bulbs from the lower brightness of the bulbs.

The various brightnesses resulting from 120v, 60v, 40v and other
lower voltages are quite easily discriminated.




I strongly suggest that Leigh (and others) acquire a supply of
matching bulbs and actually TRY these exercises before dismissing
them out of hand. No, these exercises are NOT a rigorous quantitative
'lab exercise' but they DO a VERY good job of engraining the series
and parallel connections in the students minds!

Conservation of skiers (charge), as they ski from the high
'potential' to the bottom of the slope and are then lifted back up to
the top of the slope by the ski-lift. (wall outlet)

Conservation of 'height' (loop rule), each skier MUST descend the
same vertical height regardless of which series of paths they follow.

-. .-. .-. .-. .-. .-. .-. .-. .-. .-
\ / \ / \ N / \ C / \ S / \ S / \ M / \ / \ /
`-' `-' `-' `-' `-' `-' `-' `-' `-'
Chuck Britton Education is what is left when
britton@academic.ncssm.edu you have forgotten everything
North Carolina School of Science & Math you learned in school.
(919) 286-3366 x224 Albert Einstein, 1936