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Re: photoelectric effect (clarifications)



Hi all-
Let me try to understand Savinainen's question by putting it into
a context. I suppose that there are physics teachers who discuss the
photoelectric effect as having been discovered in accordance with the
following (fictitious) history:
1. Discovery that light impinging on a metal releases free
electrons;
2. Experiment shows that the maximum electron energy is
determined by the frequency, not the intensity, of the light.
3. Valiant attempts are made to explain the result in 2.; all
failed until Einstein solved the problem by quantizing light.

The teacher discusses with the class some of the unsuccesful
calculations that were attempted in stage 2.

My question -for Savinainen only- is, is this roughly the
framework that led to your question? If so, I can comment on your
question.

Regards,
Jack

On Sun, 5 Nov 2000, Savinainen Antti wrote:

I realize that I should have defined the terms more carefully:

1) By ?classical? I refer to the 19th century physics.
2) By ?the wave theory? I refer to the Maxwell?s theory of electromagnetic waves.
3) By ?greater the intensity the greater the KE? I mean ?if the intensity is increased the kinetic energy of the ejected electrons increase?. (Please note that I?m not a native speaker of English)

My main concern was the intensity and its relation with the (maximum) kinetic energy. I found the two predictions made from the point of view of classical physics. Clarification 3 above expresses the first version which is very popular in text books. The second version states that the intensity doesn?t affect the KE because the electrons are released immediately after they have gained enough energy from the interaction with the incoming light; the KE is very low no matter what the intensity is. The question was: which version is consistent with the 19th century physics?

Of course these versions cannot be experimentally tested because both are wrong. This was already known in 1902 when Lenard found that the kinetic energy of the electron emitted from an illuminated metal was independent of the intensity of the particular incident monochromatic light. Einstein?s photon theory (1905) gave the explanation which was consistent with the experimental results.

Regards,

Antti Savinainen
Kuopio Lyseo High School/IB
Finland