Transcript Classical: electron as particle

Music, Math, and Motion
with Dr. Arun Chandra & Dr. E.J. Zita
The Evergreen St. College
Fall week 5
Tuesday 28 Oct. 2008
Overview
• Looking ahead and resources
• Your Research Projects
• Copenhagen and Quantum Mechanics
• Arun
Looking ahead
Look at Moodle:
http://elms.evergreen.edu/course/view.php?id=27#f4
Moodle details for this week
Library research resource wiki
http://www2.evergreen.edu/wikis/librarywiki/index.php?title=Music%2C_Math_%26_Motion
Your team research projects
• Due this Saturday at noon
• More guidelines on Moodle
• Time to work on them in Friday workshop
Copenhagen + program themes
• Scientific method
• Brecht: compromise for the greater good? (p.76)
• Harding: reflexivity & strong objectivity (p.72-73,
86-87);
“Jewish physics”
 morality of working on certain science
applications
• Message & communication
• Variations – different perspectives - uncertainties
Brief overview of Quantum mechanics
Classical: light as wave
Quantum: light as particle (photoelectric effect)
Classical: electron as particle
Quantum: electron as wave (H atom)
Uncertainty
Complementarity
Classical: light as wave
Quantum: light as particle
(photoelectric effect + Compton effect)
hc/l = Kmax + F
l 
h
1  cos 
me c
Classical: electron as particle
J.J. Thomson discovered electrons as particles in
1897, and shortly thereafter proposed estimating the
electron mass using E = mc2, a decade before
Einstein.
Quantum: electron as wave
Louis deBroglie predicted electron waves in 1923,
and was initially ridiculed for the idea
deBroglie was awarded the Nobel Prize in 1929.
What if we fire single electrons through
double slits, one by one?
Predict how electrons will land on the screen…
Electrons interfere as waves!
Uncertainty:
Beyond theory-laden facts: Observations can
change measurement outcomes.
Old paradigm: Who decides position is a good
thing to measure?
Complementarity
We may observe a phenomenon as wave or particle,
depending on our choice of observation method and
the situation.
Fundamental entities such as electrons and photons
are not fundamentally only waves or only particles,
but both.
Our inability to tell if an electron is a particle or a
wave is not a flaw or limit in our understanding – it is
a fact of nature. Particles and waves make sense to
humans; Nature makes electrons something more
complex.
Davisson and Germer discovered electron
waves in 1927, by accident
So did G.P. Thomson, later that year (son of J.J.
Thomson).
Davisson, Germer, and G.P. Thomson shared the Nobel
Prize in 1937.
Hydrogen atom: pre-Bohr
Plum-pudding-model … tested by Rutherford
Surprise – the atom has a nucleus!
Bohr’s Hydrogen atom:
Bohr implicitly assumed something like
resonant electron orbital wavelengths in his
successful model of the Hydrogen atom in 1913
(quantized angular momentum)
Bohr’s Hydrogen atom
Quantum mechanical uncertainty
What is the chance that an
electron with energy E2 will
be found in orbit r1?
How can QM be “true”, given all this
uncertainty?
Statistical predictions are highly uncertain for a
few particles, and very accurate & precise for
systems of many particles:
• modern electronics (e.g. semiconductors)
• diagnostics (scanning tunnelling microscope,
SEM, atomic force microscope)
• lasers
• quantum computing (coming soon?)
Particles
2. Photon
&
1. classical light waves
Newton’s corpuscles, Einstein’s PE
1. Classical electrons
Waves
Young’s diffraction
2. deBroglie’s theory
Davisson & Germer’s experiment
Bohr’s H atom
Frayn’s model:
Bohr ≈ nucleus
Heisenberg ≈ electron
Musical models:
Gabor’s ♫ particles
Fourier’s ♫ waves
Frayn’s atom
How to make decisions, in the
face of uncertainty?
“The idea that the value of pursuing the truth
rests on the possibility of certainty is a
myth.”
(Lynch, True to Life: Why truth matters, p.27)
Liese Meitner and fission
Lise Meitner was part of the team that discovered nuclear fission, an
achievement for which her colleague Otto Hahn was awarded the Nobel Prize.
Meitner is often mentioned as one of the most glaring examples of scientific
achievement overlooked by the Nobel committee.[2][3][4] A 1997 Physics Today
study concluded that Meitner's omission was "a rare instance in which personal
negative opinions apparently led to the exclusion of a deserving scientist" from
the Nobel.[5]
Gamow-Bethe-Weizsacker and the
liquid drop model of the nucleus
The liquid-drop model in nuclear physics was originally proposed by George
Gamow and developed by Hans Bethe and Carl von Weizsäcker in the 1930s.
It treats the nucleus as an incompressible fluid of protons and neutrons bound
together by the strong nuclear force. It treats the nucleus as an incompressible
fluid of protons and neutrons bound together by the strong nuclear force.
http://demonstrations.wolfram.com/NuclearLiquidDropModelAppliedToRadioacti
veDecayModes/
Resources for images and info
http://www.cobalt.chem.ucalgary.ca/ziegler/educmat/chm386/rudi
ment/tourquan/tourquan.htm
http://www.corp.att.com/attlabs/images/wave1.jpg
http://physics.ucsd.edu/was-sdphul/labs/2dl/exp6/exp6-BACK.html
http://www.randomfate.net/MT/category/humor/
http://192.107.108.56/portfolios/s/segaloff_r/instrucd
esign/final/jjthom.htm
http://www.windows.ucar.edu/tour/link=/physical_s
cience/physics/atom_particle/electron.html
Many other images from Giancoli’s Physics text, or public domain online.