Transcript Classical Physics at the End of the 19th Century

Classical Physics at the End of the 19th Century
Toward the close of the nineteenth century it appeared
as if the penultimate chapter in physics had been written.
There were indications that the final chapter would be
little more than the working out of details of fundamental
theories and their applications to problems in physics,
chemistry, engineering, and hopefully, in all fields of
human endeavor. In fact, a well-known physicist was led
to make the remark that all that remained to be done in
physics was the calculation of the next decimal point.
Sir Isaac Newton (1702) by Godfrey Kneller
The twentieth century opened on a scientific world in
which all physics appeared to be encompassed within the
mechanics of Newton and the electromagnetic theory of
Maxwell. The labors of many mathematicians and
physicists had extended newtonian mechanics to an
elegance that appeared to lack little, if anything, in
perfection. By the use of Newton’s laws and certain of
their generalizations, one could carry out very precise
calculations concerning the motions of astronomical
bodies and the behavior of machines. Indeed, by purely
theoretical calculations, Leverrier and Adams in 1846
used the known perturbations of the motion of Uranus
to predict the existence of the then unknown planet
Neptune.
Elementary Quantum Chemistry
Frank L. Pilar
Wave Behavior of Light - Young’s Double Slit Expt.
Diffraction of Waves
Slit >> l
Interference
Slit ~ l
Thomas Young (1773 – 1829)
Augustin Jean Fresnel (1788 – 1827)
An interesting triumph of the wave theory was an experiment
suggested to Fresnel by Poison, who sought to discredit the
wave theory. Poison noted that if an opaque disk is illuminated
by light from a source on its axis, the Fresnel wave theory predicts
that light waves bending around the edge of the disk should
meet and interfere constructively on the axis, producing a bright
spot in the center of the shadow of the disk. Poisson considered
this to be a ridiculous contradiction of fact, but Fresnel’s
immediate demonstration that such a spot does in fact exist
convinced many doubters that the wave theory of light is
valid.
Physics
Paul A. Tipler
Electromagnetic Theory
Michael Faraday (1791 – 1867)
James Clerk Maxwell (1831 – 1879)
Heinrich Hertz (1857 – 1894)
The Ultraviolet Catastrophe
http://breeze.nmt.edu/st589dchemnatblackbody/
Lord Rayleigh (1842 – 1919)
James Jeans (1877 – 1946)
After a few weeks of the most strenuous
labor of my life, the darkness lifted and
a new, unimagined prospect began to
dawn.
Max Planck (1858 – 1947)
The Photoelectric Effect
Einstein’s equation was a bold prediction,
for at that time there was no evidence that
Planck’s constant had any applicability
outside of blackbody radiation and there
were no experimental data on the [kinetic
energy] as a function of frequency.
Physics by Paul A. Tipler
Albert Einstein (1879 – 1955)
Robert Millikan (1868 - 1953)
Wave – Particle Duality
The Double Slit Expt. Again
Atomic Structure - Gold Foil Experiment
Ernest Rutherford (1871 – 1937)
One day Geiger came to and said, “Don’t you think that young Marsden,
whom I am training in radioactive methods, ought to begin a small
research?” Now I had thought that too, so I said, “Why not let him
see if any alpha particles can be scattered through a large angle?” I may
tell you in confidence that I did not believe that there would be, since
we knew the alpha particle was a very fast massive particle, with a great
deal of energy, and you could show that if the scattering was due to the
accumulated effect of a number of small scatterings the chance of an alpha
particle being scattered backward was very small.
Then I remember two or three days later Geiger coming to me in
great excitement and saying, “We have been able to get some of
the alpha particles coming backwards…” It was quite the most
incredible event that has ever happened to me in my life. It was
almost as incredible as if you fired a 15-inch shell at a piece of
tissue paper and it cam back and hit you.
Neils Bohr (1885 – 1962)
Postulates
• Certain orbits are stationary.
• Photon emission occurs upon orbital trans.
• Angular momentum is quantized.
Matter Waves
Louis de Broglie (1892 – 1987)
L. H. Germer
C. J. Davisson
…studying electron scattering from a nickel target at Bell Laboratories. After heating
the target to remove an oxide coating that had accumulated during an accidental
break in the vacuum system, they found that the scattered-electron intensity as a
function of the scattering angle showed maxima and minima. Their target had
crystallized, and by accident they had observed electron diffraction.
Physics by Paul A. Tipler
Constructive Interference
(Standing Wave)
Destructive Interference
http://www.youtube.com/watch?v=_S7-PDF6Vzc
Hamiltonian Mechanics
H = T + V
William Hamilton
(1805 – 1865)
The Wave Equation
The wave function contains all possible
information about a system, so instead of
speaking of “the state described by the
wave function Y,” we simply say “the
state Y.”
Quantum Chemistry by Ira N. Levine
Erwin Schrodinger (1887 – 1961)
Quantum mechanics does not say that an electron is
distributed over a large region of space as a wave is
distributed. Rather, it is the probability patterns
(wave functions) used to describe the electron’s
motion that behave like waves and satisfy a wave
equation.
Quantum Chemistry by Ira N. Levine
Max Born (1882 – 1970)