Efeito fotoelétrico na perspectiva da teoria de Kuhn

Colóquio na UERN, 24/8/2016
Carlos Alberto dos Santos
Professor Visitante
Departamento de Ciências Exatas e Naturais
Univ. Federal Rural do Semi-Árido
Mestrado Nacional Profissional de Ensino de Física
cas.ufrgs@gmail.com

http://pt.slideshare.net/casifufrgs/
cas.ufrgs@gmail.com

Colóquio na UERN, 24/8/2016cas.ufrgs@gmail.com

p. 19

p. 24

Quebra de paradigma
Revoluções
Anomalias &
Crises

Descoberta da
garrafa de Leyden
Anomalias
Descoberta dos
raios X
Ef. fotoelétrico
Radiação de
corpo negroDescoberta da
radioatividade
Descoberta do
oxigênio

Hallwachs Stoletov Righi
Corpos
metálicos
irradiados com
luz ultravioleta
adquirem carga
positiva.
Lei Stoletov: a
fotocorrente é
proporcional à
intensidade da
luz.
A fotocorrente é
composta de
moléculas do ar
dissociadas após
contato com a
superfície
irradiada.
1888 - 1890

O que Lenard fez
ente 1889 e 1898

1889: Lenard & Wolf. Pulverização de substâncias sob a
ação de luz ultravioleta. Annals der Physik, v. 37.
1899: Produção de raios catódicos pela luz ultravioleta.
Annals der Physik, v. 2.
1902: Sobre o efeito fotoelétrico. Annals der Physik, v. 8.
Bibliografia de Lenard sobre o EF

Colóquio na UERN, 24/8/2016http://www.nobelprize.org/nobel_prizes/physics/laureates/1905/lenard-lecture.pdf

1. A fotocorrente é proporcional à intensidade da luz
incidente, e sempre existe, por menor que seja a
intensidade da luz.
2. O potencial de corte independe da intensidade da luz.
3. Para um dado material do catodo, a velocidade
máxima, ou energia cinética máxima dos elétrons é
proporcional ao potencial de corte, e este depende do
tipo de luz.
4. A velocidade máxima dos elétrons independe da
intensidade da luz.
cas.ufrgs@gmail.com

Teoria do gatilho

Anomalias que incomodaram Lenard

Mas . . .

A intensidade
da luz variava
em função da
posição da
fonte L
Fotocorrente= f(intensidade da luz)
Deixa de lado um procedimento
usual na ciência normal. Deveria
ter investigado a relação entre
frequência da luz e velocidade
dos elétrons

[The photoelectric effect is a] comforting sign that a
physicist need not restrict himself to subjects which by
contemporary standards are already known and
explained. (Wheaton, 1978)

Colóquio na UERN, 24/8/2016http://einsteinpapers.press.princeton.edu/

http://www.fisica.ufpb.br/~romero/objetosaprendizagem/Rived/2
0EfeitoFotoeletrico/Site/Animacao.htm

Colóquio na UERN, 24/8/2016Physical Review, v.7, n.3, p.355-390, 1916

It was in I9o5 that Einstein made the first coupling of
photo effects and with any form of quantum theory by
bringing forward the bold, not to say the reckless,
hypothesis of an electro-magnetic light corpuscle of
energy hn, which energy was transferred upon absorption
to an electron. This hypothesis may well be called reckless
first because an electromagnetic disturbance which
remains localized in space seems a violation of the very
conception of an electromagnetic disturbance, and second
because it flies in the face of the thoroughly established
facts of interference.

The hypothesis was apparently made because it furnished
a ready explanation of one of the most remarkable facts
brought to light by recent investigations, viz., that the
energy with which an electron is thrown out of a metal by
ultra-violet light or X-rays is independent of the intensity
of the light while it depends on its frequency.

This fact alone seems to demand some modification of
classical theory or, at any rate, it has not yet been
interpreted satisfactorily in terms of classical theory.
A transição de um paradigma em crise
para um novo (...) está longe de ser um
processo cumulativo obtido através de
uma articulação do velho paradigma.
p. 116

Colóquio na UERN, 24/8/2016http://www.nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-lecture.pdf

In view of all these methods and experiments the general
validity of Einstein’s equation is, I think, now universally
conceded, and to that extent the reality of Einstein’s light-
quanta may be considered as experimentally established.
But the conception of localized light-quanta out of which
Einstein got his equation must still be regarded as far from
being established.

Colóquio na UERN, 24/8/2016Philosophical Magazine, t. XLVII, p.446-457, 1924

Colóquio na UERN, 24/8/2016Holton, 1999
Two final ironies: In 1950, at age 82, Millikan published
his Autobiography. Chapter 9 is entitled simply ‘‘The
Experimental Proof of the Existence of the Photon –
Einstein’s Photoelectric Equation.’’ By then, Millikan had
of course come to terms with the photon. Moreover, he
had evidently changed his mind about what he had done
around 1916. For now he wrote (pp. 101–102) that as the
experimental data became clear in his lab, they . . .

‘‘proved simply and irrefutably, I thought, that the
emitted electron that escapes with the energy hn gets
that energy by the direct transfer of hn units of energy
from the light to the electron and hence scarcely
permits of any other interpretation than that which
Einstein had originally suggested, namely that of the
semicorpuscular or photon theory of light itself.’’ In the
end, Millikan re-imagined the complex personal history
of his splendid experiment to fit the simple story told in
so many of our physics textbooks.

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