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Re: [Phys-l] two kinds of electrical charge ????????



Maybe I missed the point of the original question - which seemed to be what model a student brings to a physics class - one-fluid or two fluid. My response simply was to state that they bring neither. They are hardly "naive" if they have not encountered terminology that is obscure to almost anyone in physics who is not presented with a definition of the terms before being asked to respond.

Their automative response will always be that there are two types of charges, positive and negative. They will then go through the mantra of likes repel and unlikes attract. And I cannot imagine a student who has not gone beyond a general physics class not associating the charges with specific particles - electrons and protons. (As I said before, a rare few students are aware of fractional charge - and exotic particles.)

I asked a few others im my department whether charge should be thought of as a one-fluid or two-fluid model and they all responded with a variation of "what do you mean by that?". They were all comfortable with only needing a single number to describe charge - perhaps that concept deserves a fancy title like "one-component model", but it is hardly terminology familiar to those I spoke to.

Again, I see no disagreement here - just a need to be clear as to what level we are speaking on.

Bob at PC

________________________________

From: phys-l-bounces@carnot.physics.buffalo.edu on behalf of John Denker
Sent: Wed 8/1/2007 6:05 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] two kinds of electrical charge ????????



On 08/01/2007 03:42 PM, LaMontagne, Bob wrote:
I would go a little further - My gut is telling me that if you queried
the majority of physics faculty about a "one-component model" of
electric charge, they would respond that they have no idea what you are
talking about. I can't in my wildest imagination believe that students
entering my General Physics class have ever heard of such a concept.
They all "know" that there are two types of charges: negative electrons
and positive protons. A scarce few might mention positive and negative
quarks with fractional charges.

I think we are in one of those classic situations on the list where
everyone is saying the same thing but talking past each other.

I don't think we're all saying the same thing.

They all "know" that there are two types of charges: negative electrons
and positive protons.

I don't much mind if they say things like that as a sloppy figure of
speech ... but if they mean that to be taken seriously, I'm shocked.
That's at least two goofs removed from reality.

1) First of all, I would hope they meant to say "two types of charged
particles" rather than two types of charge. There's a hugely important
difference between "charge" as an abstraction and its embodiment in a
particular charged particle. Particles have many properties. Charge
is only one property among many. There are different kinds of particles.
but that does not mean there are different kinds of charge.

Let's be clear: "charge" is not the same thing as "charged particle".
Charge, of the sort that appears in the law of conservation of charge,
is an abstraction. There is only one kind of charge, and only one
law of conservation of charge. Conservation of charge does not even
remotely suggest that the various types of charged particles are
separately conserved.

2) Secondly, even if we shift attention from charge to charged particles,
it is not even remotely true that protons and electrons are the only
charged particles. The existence of antimatter was discovered in the
1930s. Mesons were predicted in the 30s and observed in the 40s. Quarks,
fractional electrical charges, and the color charge came along in the
60s.

Are you telling me that your colleagues, except for a scarce few,
are living 40 years behind the times? Or 70 years? Jeepers,
that's scary.

===============

My first two physics teachers were guys who did quantum chromodynamics
for a living. They knew the difference between abstractions and
embodiments. They knew the difference between charge and charged
particles. They knew first-hand that there were more than two kinds
of charged particles. They knew the difference between SU(3) and U(1).
They knew there were three kinds of color charge and one kind of
electrical charge.

In any case, we shouldn't make this an appeal to authority. I don't
much care if 99% of the community is wedded to the two-fluid model;
it wouldn't be the first time that 99% of the community was wrong.
Look at the equations already! There's only one equation for
conservation of charge, and only one type of Q that appears therein.
That Q is conserved, even in situations where the number of protons
is not conserved, as discussed in detail at
http://www.av8n.com/physics/one-kind-of-charge.htm
At some point, the figures of speech ought to be brought into
agreement with the equations.

Also note that AFAICT, nobody has offered the slightest bit of
objective evidence (theoretical and/or experimental) against the
one-component theory. PbBA is not evidence. Arguing that the
two-fluid model is consistent with some of the data is not
evidence against competing theories.

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