Re: photoelectric effect classically

[Arnulfo Castellanos Moreno <acastell@FISICA.USON.MX>]

Certainly a specification about wave theory is needed.
You can explain the photoelectric effect without the photon, but Schrodinger
equation
plus classical electromagnetic fields (as solutions to Maxwell equations)
are necessary.

Using newtonian mechanics plus classical electromagnetic fields do not give
you
the explanation of the effect.


Arnulfo Castellanos-Moreno
Departamento de Fisica
Universidad de Sonora
Hermosillo, Sonora, Mexico.



----- Original Message -----
From: Savinainen Antti <antti.savinainen@KUOPIO.FI>
To: <PHYS-L@lists.nau.edu>
Sent: Saturday, November 04, 2000 9:01 AM
Subject: photoelectric effect classically


> Dear Colleagues,
>
> I have a question on the wave theory predictions for the photoelectric
effect.  According to the wave theory only the intensity should affect
maximum kinetic energy of the ejected electrons. Increasing intensity means
increasing the magnitude of electric field vector which increases the force
exerted on an electron by the incident beam. Hence the greater KE. Another
way to look at it is to say that the greater the intensity the greater the
energy per second reaching the plate and the greater the KE.
> The frequency of the light should not affect the KE. Classically intensity
and energy density of electromagnetic wave do not depend on frequency (am I
right?).
> The explanation above is frequently given in high school and introductory
university books. But is it really correct? I started digging this because
some of my students insisted more specific information on the classical
predictions. I'll give another explanation which I found from a bit more
advanced text.
> The force exerted on an electron can be expressed as F = e(E + v cross B)
and in case of linearly polarized light E = E0sinwt and B = B0sinwt. The
electron gains energy and starts to oscillate. This takes some time. When
energy of the electron is equal or just greater than the work function it is
immediately ejected from the metal. So electron does *not* gain significant
KE and this leads to low kinetic energies no matter what intensity is used.
If intensity is greater the electron is released faster. This prediction
contradicts with the former because now greater intensity does not imply
greater KE.
> Which prediction is consistent with Maxwell's wave theory?
>
> One more question. How would the oscillation of the electron change if
unpolarized light was used? In this case the electric field (and the force)
changes direction randomly in the plane perpendicular to the propagation of
the light ray. Can the electron gain energy if the light is unpolarized?
> Regards,
>
> Antti Savinainen
> Kuopio Lyseo High School