On March 17, 1905, Albert Einstein submitted his
paper,
Über einen die Erzeugung und Verwandlung des Lichtes
betreffenden heuristischen Gesichtspunkt (
Concerning an
Heuristic Point of View about the Creation and Conversion of
Light (pdf)). This is the paper for which he received the 1921
Nobel Prize in Physics
"for his
services to Theoretical Physics, and especially for his discovery
of the law of the photoelectric effect", not for
Brownian
motion, not for special relativity, not for general relativity,
not for the famous equation
E = mc2.
Max Planck had hypothesized that energy came in discrete packets,
which he called quanta.
[T]he problems of radiation processes engaged his
attention and he showed that these were to be considered as
electromagnetic in nature. From these studies he was led to the
problem of the distribution of energy in the spectrum of full
radiation. Experimental observations on the wavelength distribution
of the energy emitted by a black body as a function of temperature
were at variance with the predictions of classical physics. Planck
was able to deduce the relationship between the energy and the
frequency of radiation. In a paper published in 1900, he announced
his derivation of the relationship .... The energy for a resonator
of frequency v is hv where h is a universal constant, now called
Planck's constant.
Max
Planck -- Biography. Planck received the 1918 Nobel Prize in
Physics for this discovery:
"in
recognition of the services he rendered to the advancement of
Physics by his discovery of energy quanta".
Maxwell's equations and classical thermodynamics assumed that the
range of possible energies was continuous, consistent with the view
that electromagnetic energy propagated through space as
waves.
Physicists knew that when ultraviolet light shined upon certain
metals, electrons were ejected from the material. But the number of
electrons ejected depended on the intensity of the light, and the
energy of the electrons depended on the frequency, not the
intensity, of the light, facts difficult to explain under classical
physical theory, but not difficult if the ultraviolet light and the
electrons were quanta, and that only certain energy states were
permitted: the intensity of the light is the flux (concentration,
or number passing through an area) of the quanta, and the energy is
Planck's equation.
Sources:
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