Download Ch. 40 - UMD Physics

Chapter 40
Serway & Jewett 6th Ed.
Approximate Total Absorption Cavity
Stefan- Boltzman Law
I = T4
= 5.6699  10-8 W/m2-K4
Ultraviolet Catastrophe
I
2ck BT
4
Classical expression
Quantized Energy Levels
of a Harmonic Oscillator
Photoelectric Effect
Fig 40-9, p.1292
Photoelectric Effect
Table 40-1, p.1294
Electrons interacting with light
Classical Picture

 
F  qv  B  qvB kˆ
Just dipole radiation
independent of !
Electrons interacting with light
Quantum Picture
 'o 
h
1  cos 
me c
Compton
Scattering
Atomic Spectra
Hydrogen
Nitrogen
Balmer’s Realization
DeBroglie Wavelengths
The Davisson-Germer experiment showed that
electrons exhibit the DeBroglie wavelength given by:
k1 – k2 = k
k1 + k2 = k
1 – 2 = 
1 + 2 = 
Wavepacket
 A cosw t 
i
i
i
Delayed Choice
Depending on how we do the
experiment we determine what happens!
Superposition States
  c1 1  c2 0
=
+
=
Measurement
One and only one of
or
Photons are emitted on opposite sides of the pump beam, along two
cones. One of cone has horizontal polarization and the other of has
vertical polarization. Photon pairs emitted along the intersections
of the cones are entangled in polarization -- each photon is
individually unpolarized, and yet the photons necessarily have
perpendicular polarizations, no matter how far apart they are!
http://www.physics.uiuc.edu/People/Faculty/profiles/Kwiat/index.html
Quantum Weirdness!
What is Schrodinger's Cat Paradox?
Schrodinger's Cat (in his own words)
"One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following
diabolical device (which must be secured against direct interference by the cat): in a Geiger counter there is a
tiny bit of radioactive substance, so small that perhaps in the course of one hour one of the atoms decays, but
also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases
a hammer which shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour,
one would say that the cat still lives if meanwhile no atom has decayed. The first atomic decay would have
poisoned it. The Psi function for the entire system would express this by having in it the living and the dead cat
(pardon the expression) mixed or smeared out in equal parts. It is typical of these cases that an indeterminacy
originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then
be resolved by direct observation. That prevents us from so naively accepting as valid a "blurred model" for
representing reality. In itself it would not embody anything unclear or contradictory. There is a difference
between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks." -- Erwin Schrodinger
Translation by John D. Trimmer
Basically what Schrodinger is saying is that because of the way the experiment is set up, the cat has a 50%
chance of being alive, and a 50% chance of being dead. It is just as likely that the cat is alive as that it is dead, so
Schrodinger said that until the box is opened, the cat is both alive and dead. This is obviously false, the cat cannot
be both alive and dead at the same time. This problem is meant to illustrate a theory of quantum mechanics
called "indeterminacy." Indeterminacy says that there can be more than one correct answer to a problem which
physically can only have one answer. Schrodinger came up with this illustration to demonstrate that there was a
problem with this theory of quantum mechanics.