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Re: Collisional excitations



The Franck-Hertz experiment is well known ("by those who know it well", as
one of my old profs used to say) and is featured quite often in a standard
physics curriculum, typically in a 3rd semester introductory course (at my
school this semester is call "introduction to modern physics" and actually
isn't sequentially numbered relative to the standard 1st year course. The
experiment is also oftened mentioned in an upper division modern physics or
quantum mechanics course. (Of course, curricula vary, as does individual
mileage)

A few intermediate to elementary references.

McGervey's "Introduction to Modern Physics", page 87 in my older edition.
Kranes's "Modern Physics", 2nd ed., page 195.
Rohlf's "Modern Physics from alpha to Z_nought", page 83.



Joel Rauber
Joel_Rauber@sdstate.edu


-----Original Message-----
From: phys-l@lists.nau.edu: Forum for Physics Educators
[mailto:PHYS-L@lists.nau.edu]
Sent: Tuesday, September 19, 2000 8:29 AM
To: PHYS-L@lists.nau.edu
Subject: Re: Collisional excitations



Franck-Hertz, eh? I'd heard of it but never read the experiment.
Thank you all for your comments.

Philip Zell


______________________________ Reply Separator
_________________________________
Subject: Re: Collisional excitations
Author: "phys-l@lists.nau.edu: Forum for Physics Educators"
<PHYS-L@lists.nau.edu> at internet
Date: 9/19/00 5:03 AM


That is right. Positive energy values as those of the
exciting particle
are not quantised. They are continuous.

regards,

Sarma.
They are continuous.
At 04:20 PM 9/18/00 -0400, you wrote:
-----Original Message-----
From: phys-l@lists.nau.edu: Forum for Physics Educators
[mailto:PHYS-L@lists.nau.edu]On Behalf Of Joel Rauber
Sent: Monday, September 18, 2000 3:23 PM
To: PHYS-L@lists.nau.edu
Subject: Re: Collisional excitations


Isn't quantization of energy during collisions one of the
lessons of the
Franck-Hertz experiment?

Joel Rauber

Yes--Franck_Hertz is evidence of the quantization for the energy
_absorbed_
by the target atoms, but does not show that the initial energy of the
incident electron is quantized. As long as the incident electron has
sufficient energy to cause the target atom to make the
transition, there
is
a non-zero probability for the interaction to take place.
The probability
is
measured using the concept of cross section.

The plot of cross section vs. incident electron energy is known as an
excitation function. That function always starts at zero,
rises fairly
quickly, and then drops off at various rates, typically
between 1/E and
1/E^3 at high energies. The slope of the high energy end
depends on the
particular transition being induced in the atom.

(My thesis title was something like "The electron impact
excitation of
krypton and xenon.")


--
John E. Gastineau john@gastineau.org
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