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Re: photoelectric effect (clarifiations)



Dear Jack,

thanks for your illuminating views. In fact I used to teach the topic
approximately the way you described (i.e. Einstein *predicted* that
max KE of the photoelectron is dependent on the frequency of the
incident light). I didn’t invent ”the fictitious history”; I happened
to find it in some physics books. For instance, Advanced Level
Physics by Nelkon & Parker (sixth edition) states that (p.845):

”In 1902 Lenard found that the velocity of kinetic energy of the
electron emitted from an illuminated metal was independent of the
intensity of the particular incident monochromatic light. It appeared
to vary only with the wavelength or frequency of the incident light.”

The concept of electron was already known at the time because Thomson
measured the ratio e/m of ”cathode ray particles” in 1897.

A bit later Nelkon & Parker state (p. 846):

”In 1905 Einstein suggested that the experimental results in
photoelectricity could be explained by applying a quantum theory of
light.”

Remarks similar to this exist in some other books as well. It seems
to contradict what you said in the previous posting:

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. THAT WAS
EINSTEIN'S PREDICTION, >later borne out by experiment.

On the other hand it is possible that the writers do not refer to the
Lenard’s experiments when they say that ”It appeared to vary...”. But
they state explicitly that Lenard knew in 1902 that the KE of the
ejected electrons did not depend on the intensity of the
monochromatic light and that Einstein knew about these experimental
results at the time he published his paper on the photon theory in
1905.

Nelkon & Parker is not a book on history of physics (it is a British
A-level -- high school -- book) so it is quite possible that it
contains erroneous information on the historical context. I haven’t
consulted the original papers. Perhaps you could help to clear the
matter?


Best regards,

Antti Savinainen
Finland