I don't think of this task as a test. It is rather a very good
engagement exercise. When my pre-service eleds do it, many go through
three stages.
First, since most of them think of batteries and bulbs in terms of a
tranfer or delivery, they connect the one wire to the bulb and to the
battery and of course nothing happens.
Then they note that the battery has two ends and begin to think of ways
to incorporate the two ends. Thats when they are likely to connect the
wire directly across the battery.
By the way, to forestall the uncomfortable hot sensation they get at the
battery wire connection I use somewhat worn out AA batteries, which will
still light the bulb but won't deliver enough current to make the
connection hot.
Once the figure they can't light the bulb by making one connection to
the bulb, I sometimes have to raise the question of whether or not there
are two "ends" of the bulb just as there are two ends to battery and to
the wire.
Eventually they find 4 different configurations to light the bulb, but
for them them the bulb is still a black box. This is a very
instrumental exercise, if I may use this philosophical term, the only
really new insight is that there is a need for some sort of circulation.
Just for the record , this is McDermott's Physics by Inquiry.
I think several things are happening in this exercise. First the
students are getting comfortable with bulbs and wires and batteries.
Second they are beginning to see that a delivery model does not work,
but that their actions are predicated on it. They begin to see that
they need to think in terms of a circulation model.
It is a good place to begin, but not a good test since so many pieces
have to go together to be successful. By the way, seeing the bulb light
is exciting for these students....so there is a nice reward for success.
One other point. This year I gave a pretest that had a series of
pictures showing ways the bulb, wire, and battery might be connected,
and asked them to predict which would light. The students got about
half of them correct, with some configurations consistently wrong.
However, the pretest seemed to have no effect on their ability to light
the bulb, because the process for the students was essentially the same
as it had been when I didn't give the pretest. They didn't seem to pick
up any clues for how to do it successfully, and it didn't even give them
clues on different ways to connect the three pieces together.
cheers,
joe
--
Joseph J. Bellina, Jr. Ph.D.
574-284-4662, 4968
Saint Mary's College
Dept. of Chemistry and Physics
Notre Dame, IN, 46556