Chronology | Current Month | Current Thread | Current Date |
[Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
Electrostatic charge transfer is not well understood, and I've seen
frequent mention that, for some types of materials, "frictional charging"
is probably caused by the transfer of ions both neg and pos types, not of
bare electrons.
The term some types of materials, also implies that for many other materials
the one way model is probably operative.
While frictional charging may
involve some positive transfer, the two way idea is then generalized by the
students to mean that the positive charges then move around a conductor as
well as the negative charges moving.
Sticking to the case of electron movement creates fewer problems,
and is much better pedagogy.
That being
said, one must always admit to students that the real world is more complex
and messier than the models we construct to try to understand it. In either
case the currently accepted standard simplified model of electrostatic
charging is a one way model.
One can certainly say that current is the flow of both positive and negative
particles in the case of a solution, such as NaCL in water, however in the
case of a copper wire, the copper generally stays in place and the electrons
flow. The case of a semiconductor is quite subtle.
The always and forever model is clearly wrong with respect
to the always, but is a very good model when dealing with conductors.
When you charge objects by rubbing what fraction of the electrons in the
positively charged object are transferred to the negatively charged
substance: a. 100%, b. 50% c. 10%, d. 1% e. an extremely small fraction
A few students will answer e, and a fair number will answer a.
The correct answer is generally only given by some students who have tested
as formal thinkers.
Once students have accommodated the simpler models, then more complex models
can be tackled. The pedagogy for doing that is not as clearly defined, and
will be researched. I will also admit that I do not know of any research
which compares using an electron flow model vs. a conventional current
model. It should be possible to compare these as to the ability of the
students to form a realistic stable useful model. Is anyone doing this
research???
Do your students say they have no idea why plants have flowers, or think
that the water on the outside of a cold glass diffused through the glass?
Mine do even after having bio. and chem. I would bet that many of yours
have these problems. Let us tackle the basics first!