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Re: photoelectric effect (clarifications)



Jack Uretsky wrote:
Consider. Hertz observed (~1885, I think) sparks emanating from
metal surfaces that were exposed to uv light while being subject to
strong electric fields. It wasn't until 15 years later that JJ Thompson
determined that cathode rays had corpuscular constituents with an e/m
that we now ascribe to the electron. It was not understood at that time
that a metal could be described as a sea of electrons. And, most
importantly, it had not been determined, at the time of Einstein's paper,
that the maximum energy of a photoelectron was dependent on the frequency
of the incident light.
So Einstein's genius encompassed more than just the quantization
of light - it encompassed an insight into the nature of electrical
conduction in metals, the nature of the metallic state (including, I
believe, the concept of the "work function"), and a view of the
interaction of electromagnetic waves with charged corpuscles.

Aside from the question of whether Lenard's 1902 observations indicated
an understanding that electrons left metals, we also have Drude's 1900
model of metals as a gas (or sea, if you like) of electrons. And such a
model seems to immediately imply an energy barrier which electrons must
surmount in order to leave the metal. So I think that perhaps Jack is
given Einstein more credit than is due.

Note also that since the applicable 19th century theory involves
electrons treated with the kinetic theory of gasses, problems of
changing orbital frequency (such as John Denker has suggested) do not
arise. The trajectory of an otherwise free charged particle in an E&M
wave is a mess, I think. But as long as the power per electron is less
than the workfunction divided by the mean free time, we are just heating
up an electron gas. An argument looking at a sole electron absorbing
energy would be inconsistent with this model. An argument based on a
sole electron being accelerated by an electric field would require the
above power threshold be crossed, but would be incomplete (within this
model) since it ignores the heating effect.

--
Dr. James McLean phone: (716) 245-5897
Dept. of Physics and Astronomy FAX: (716) 245-5288
SUNY Geneseo email: mclean@geneseo.edu
1 College Circle
Geneseo, NY 14454-1401


Postscript:
I was amused by the following quote and reply:

John Denker wrote:
At 04:05 PM 11/5/00 +0200, Savinainen Antti wrote:
The question was: which version is consistent with the 19th century physics?

Of course these versions cannot be experimentally tested because both are
wrong.

Exactly! Both are wrong.

Of course, John intended to be replying to Antti's second sentence, and
by "wrong" he meant "inconsistent with reality." But by including
Antti's first sentence, he left ample evidence that he was not actually
addressing Antti's question.