Download 1. Modern Physics

Modern Physics
This isn’t Newton’s Physics!
Democritus – 400 BC

First known person to advance the idea
of “atoms” as building blocks of matter.
Dalton – 1800


First name: John
Established the likelihood that elements
consist of basic structural units (like
Democritus’ atoms).
Michelson - 1879


First name: Albert
Measured the speed of light
(accurately) for the first time.
“Luminiferous Ether”

It was known that light was a wave
(interference, diffraction, etc), yet it
was able to travel through space which
apparently contained no continuous
mass. It was, therefore, assumed that
some undetectable mass existed in
space, the luminferous ether.
Michelson/Morley - 1887


Michelson, in combination with Edward
Morley, conducted a famous experiment
that bears their names to detect the
luminiferous ether.
No ether was detected
Hertz - 1887



First name: Heinrich
Discovered the Photoelectric Effect
(accidentally).
Shining light on certain metals caused
an electrical current.
Thompson – 1897


First name: JJ (Joseph John)
Discovered the existence of electrons as
particles. Formerly known as “cathode
rays”.
Planck - 1900




First name: Max
Radiating objects (black-body) emit specific
colors regardless of temperature. EM theory
predicted an “ultraviolet catastrophe”.
Planck noted that blending two separate (and
apparently unrelated) theories resolved the
problem.
Concluded that light must act like particles
(photons) which contained fixed (quantized)
amounts of energy related to their frequency
(E=hf). Referred to as the Quantum Theory.
Einstein - 1905




First name: Albert
Published his Theory of Special Relativity
Measurement of time wouldn’t be the same
for all observers, but would instead be related
to their relative motions.
Energy and mass were interchangeable
(E=mc2)
Thompson – 1905(?)

“Plum-pudding” Atomic Model
Millikan - 1910


First name: Robert
Measured the charge on the electron in
the famous experiment that bears his
name.
Rutherford – 1911


First name: Ernest
Gold Foil experiment
Gold Foil Experiment:
Rutherford’s Conclusions:




Most positive charge and mass is in a small,
centralized region (nucleus).
A consequence of this is that there must be
positive particles (protons).
Electrons are “outside” the nucleus.
Suggested that neutral particles consisting of
proton plus electron might also be found (in
the nucleus).
Bohr - 1913




First name: Niels
Followed up Rutherford’s experiment by
suggesting a “planetary” model for the atom
(electrons as “planets”; nucleus as “sun”).
“Orbits” had specific energies.
He successfully predicted the energy levels
for hydrogen atoms.
Demo
Einstein - 1915


Explained the photoelectric effect by using
Planck’s Quantum Theory.
Ironically, this explanation led to the
widespread acceptance of Planck’s Quantum
Theory, and Einstein spent much of his later
life seeking to circumvent its statistical nature
(“GOD doesn’t play dice”).
Photoelectric Effect


Energy is required to release electrons from a
photoemissive metal (ionization energy).
If light is a wave, then increasing brightness
should release electrons.
Photoelectric Effect (cont.)


Energy is required to release electrons from a
photoemissive metal (ionization energy).
If light is a photon, then increasing frequency
should release electrons.
Millikan - 1915


Verified Einstein’s explanation of the
photoelectric effect
Determined the value of Planck’s
constant
KEmax
W0
f0
f
Einstein - 1916

Published his General Theory of
Relativity which led to the prediction of
the existence of black holes, gravitywarped space, gravity-deflected light,
etc.
Compton - 1922



First name: Arthur
Photons colliding with electrons caused
the electrons to be deflected, and the
process conserved both energy and
momentum.
Photons act as if they have mass.
de Broglie - 1924



First name: Louis
Suggested that just as light waves could
behave like particles (photons),
particles could similarly behave like
waves, with wavelength related to
momentum.
=h/mv
Schroedinger - 1926



First name: Erwin
Developed wave equations to define particles
(electrons). Solutions to the wave equations
defined the characteristics of the particles.
Led to the Electron Cloud Model of the atom
and removed the limitations inherent in
Bohr’s model of the atom.
Heisenberg - 1927



First name: Werner
Published his Uncertainty Principle. It
was impossible to determine both the
momentum AND position of a
particle/wave.
Measuring affects the measurements.
Chadwick – 1932


First name: James
Discovered the neutron
Gell-Mann and Zweig - 1964


First names: Murray and George
Proposed that nucleons were composed
of smaller particles (quarks)
Friedman and Kendall - 1968


First names: Jerome and Henry
Provided the first experimental evidence
for the existence of quarks.