Re: Cosmology

[Brian Whatcott <betwys1@SBCGLOBAL.NET>]

At 12:54 PM 6/21/2004, BC, you wrote:
> I've heard the Nobel committee awarded E. for the PE effect because of
> its commercial use.   Tho Eddington's eclipse confirmation was before
> the award, Arrhenius' presentation speech includes only a short
> paragraph to relativity, and another to Brownian motion.
>
> http://www.nobel.se/physics/laureates/1921/press.html

I extracted a fragment of Arrhenius's speech (Einstein was not present)

" ...the photoelectric effect. This latter had been discovered by the
 famous physicist Hertz in 1887. He found that an electrical spark
passing between two spheres does so more readily if its path is
illuminated with the light from another electrical discharge.
 A more exhaustive study of this interesting phenomenon was
carried out by Hallwachs who showed that under certain
conditions a negatively charged body, e.g. a metal plate,
illuminated with light of a particular colour - ultraviolet has the
strongest effect - loses its negative charge and ultimately
 assumes a positive charge. In 1899 Lenard demonstrated
the cause to be the emission of electrons at a certain velocity
 from the negatively charged body. The most extraordinary
aspect of this effect was that the electron emission velocity
 is independent of the intensity of the illuminating light, which
is proportional only to the number of electrons, whereas the
velocity increases with the frequency of the light. Lenard
stressed that this phenomenon was not in good agreement with
the then prevailing concepts.

An associated phenomenon is photo-luminescence, i.e.
phosphorescence and fluorescence. When light impinges on a
substance the latter will occasionally become luminous as a
result of phosphorescence or fluorescence. Since the energy
of the light quantum increases with the frequency, it will be
obvious that a light quantum with a certain frequency can only
give rise to the formation of a light quantum of lower or, at most,
 equal frequency. Otherwise energy would be created.
The phosphorescent or fluorescent light hence has a lower
 frequency than the light inducing the photo-luminescence.
This is Stokes' rule which was explained in this way by
Einstein by means of the quantum theory.

Similarly, when a quantum of light falls on a metal plate it can
 at most yield the whole of its energy to an electron there.
A part of this energy is consumed in carrying the electron out
into the air, the remainder stays with the electron as kinetic
energy. This applies to an electron in the surface layer of the
metal. From this can be calculated the positive potential to
which the metal can be charged by irradiation. Only if the
quantum contains sufficient energy for the electron to
perform the work of detaching itself from the metal does
the electron move out into the air. Consequently, only light
having a frequency greater than a certain limit is capable
 of inducing a photo-electric effect, however high the intensity
of the irradiating light. If this limit is exceeded the effect is
 proportional to the light intensity at constant frequency
. Similar behaviour occurs in the ionisation of gas molecules
and the so-called ionisation potential may be calculated,
provided that the frequency of the light capable of
ionising the gas is known."




Brian Whatcott    Altus OK    Eureka!