🚀 go-pugleaf

In article <67lsh9$5br$1@agate.berkeley.edu>,
Martin Green <testware@pangea.ca> wrote:

[stuff deleted]

>> I think Martin Green is confusing "evidence for" with "mathematical
>> proof of".  I believe it is intellectually honest to tell high-school
>> students that Planck's black-body formula, and the photo-electric
>> effect, and a bunch of other stuff, lead to our current picture......
>
>If it's the Compton effect which demonstrates that light is made of
>particles, then why is it "intellectually honest" to tell high school
>students that the photo-electric effect cannot be explained by classical
>waves?

I think that the point is that most high school/ non-calculus texts
go through a list of experimental evidence which is more "naturally"
explained by a photon hypothesis (rather than classical E&M). Then
they end with the Compton effect which as far as I know can *only*
be explained by a photon theory of light. For example I recently
got a free copy of Cutnell&Johnson's "Physics" (which is
roughly the same level as Giancoli's "Physics") and when it does
QM they start with Blackbody radiation, photoelectric effect,
and then end with the Compton effect. Maybe the first two could be
explained via classical E&M, but when taken all together and
including the Compton effect, I think one doesn't have anyway
to wiggle out of the photon hypothesis. Also one might argue that
even without the Compton effect the photon hypothesis is easier or
more "natural". One possible reason to say that the photo-electric
effect is experimental "proof" of the photon hypothesis is that 
(at least for the high school/non calculus classes) it's just
more trouble than it's worth to explain all the caveat's and
possible side tracks that one could go into, when in the end 
one will talk about the Compton effect and conclude that "Yes
the photon hypothesis is the only thing that seems to work"
(as far as I know).  

>I took two full-year grad-level courses in quantum mechanics. I think
>that's as much QM as anyone takes on the way to becoming a physics
>professor. We didn't cover the Compton effect, so I can't say whether or
>not it could be explained by classical waves. All I know is that the
>traditional explanation of how the photo-electric effect does or doesn't
>work is based on ignorance of the laws of classical electromagnetics.
>
>Martin Green

I looked in the index of Schiff and indeed he doesn't mention the
Compton effect (also Merzbacher doesn't do the Compton effect
from what I recall). So it seems to be true that if one takes
the core grad courses (two semesters of QM is the usual right ?) 
then the Compton effect would be missed. However, one can
easily get a not too bad understanding of the Compton effect
just from the photon hypothesis and some kinematics (for
example Serway has a "Physics for scienetist and engineers
with modern Physics" where he goes through the Compton effect,
pgs. 1153-1156 ). A more advanced treatment of the Compton
effect will usually be found in some third semester QM
course taught from some text like Sakaurii's "Advanced QM"
or Holstein's "Topics in Advanced QM". From my own experience
it does seem to be true that most students don't end up taking the
advanced QM courses, but rather opt to start working in their
labs. 



Doug