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Transcript
Introduction to the experiments of
Physics 407
Franck-Hertz
Franck-Hertz experiment:
confirmation of quantized atomic energy levels
1st evidence: Spectrum from a low-pressure mercury lamp
Franck-Hertz
Sketch of Franck-Hertz Apparatus
Collecting plate is slightly
Positively charged grid negative compared to grid –
accelerates electrons
so only those electrons
above an energy threshold
will reach it.
+
Heated cathode
produces electrons
after Krane
accelerating voltage
Current from collector
measured as a
function of
accelerating voltage.
Voltage between peaks corresponds to
excitation energy
4.9 V
Franck-Hertz
Hall effect
Hall effect with negative charge carriers
+
Fm = magnetic
force on
negative charge
carriers
Direction of conventional
Electric current
Fe = electric force
from charge
buildup
http://hyperphysics.phy-astr.gsu.edu
Hall effect
Hall effect in semiconductors
Dominated by negative carriers.
Dominated by positive carriers.
Johnson noise
Johnson Noise
+
Cause:
Thermal motion
 0 Vrms??
Johnson noise
Johnson Noise:
way to measure Boltzmann’s constant
JB Johnson, Physical Review 32 (1928) 97
Brownian motion
Brownian motion:
more evidence for thermal motion
Perrin’s Atoms
Nakroshis et al. AJP 71 (2003) 568
Chaos
State space of a dynamical system
IDEAL
FRICTION
James P. Crutchfield, J. Doyne Farmer, Norman H. Packard, and Robert S. Shaw
SCIENTIFIC AMERICAN DECEMBER, 1986 VOL. 254 NO. 12, 46-57.
Chaos
10,000 red dots
Chaos
Chaotic behavior
is characterized by
divergence of
nearby trajectories.
Lyapunov exponent
is a measure of this
divergence.
2 slit interference, one photon
Two-slit interference one photon at a time:
grappling with wave/particle duality
Single photon interference: “a phenomenon which is impossible, absolutely impossible to
explain in any classical way, and which has in it the heart of quantum mechanics. In
reality, it contains the only mystery.” - Richard Feynman
http://www.blacklightpower.com/theory/DoubleSlit/
2 slit interference, one photon
Faraday effect
The Faraday effect
Faraday effect
Right and left circularly polarized light have
different indexes of refractions
http://www.ifm.liu.se/~ulfek/viz/
Faraday effect
Verde constant depends on wavelength
Jain, Am. J. Phys. 67, August 1999, 714
Zeeman effect
The Zeeman effect
Zeeman effect
The Zeeman effect: Mercury energy levels
Zeeman effect
Fabry-Perot distinguishes wavelengths
Optical Pumping
Optical pumping
F=2
5P1/2
F=1
795 nm
light
F=2
5S1/2
462 MHz
F=1
Hyperfine
mF
2
1
0
-1
-2
B increases
Nuclear magnetic resonance
NMR
B-field
Electron Spin Resonance (ESR)
Organic salt, DPPH
Microwaves
Microwaves
www.microwaves101.com
Compton scattering: light as a particle
Muon Lifetime
Muons are produced in cosmic rays
www.lanl.gov
Muon Lifetime
Properties of the Leptons
Particle
Symbol
Antiparticle
Rest mass
MeV/c2
L(e)
L(muon)
L(tau)
Lifetime
(seconds)
Electron
e-
e+
0.511
+1
0
0
Stable
Neutrino
(Electron)
νe
νe
0(<7 x 10-6)
+1
0
0
Stable
Muon
μ-
μ+
105.7
0
+1
0
2.20x10-6
Neutrino
(Muon)
νμ
νμ
0(<0.27)
0
+1
0
Stable
Tau
τ-
τ+
1777
0
0
+1
2.96x10-13
Neutrino
(Tau)
ντ
ντ
0(<31)
0
0
+1
Stable
www.hyperphysics.phy
Muon Lifetime
Decay of muon proceeds through the
weak interaction
Muon Lifetime
Muons stopped by plastic scintillator
plastic scintillator
photo-multiplier tube
http://alpha.sci.osaka-cu.ac.jp/grapes3
Muon Lifetime
Typical muon-electron pulses from the
photomultiplier tube
www.prestoncoll.ac.uk
Plasma
Plasma: “the 4th state of matter”
Most common state for the visible
matter in the universe.
hyperphysics.phy-astr.gsu.edu
Plasma
Langmuir probe used to measure electron
temperature
Langmuir probe on Cassini/Huygens
(Photo: IRF Uppsala)
Cassini approaches Saturn
(Artist's impression: NASA)
Cavendish experiment:
measure of G, gravitational constant
http://fas.harvard.edu
2 equilibrium positions double the accuracy
Experiment 1 order
12:30 Douglass, Scott
12:45 Marcu, Diana M.
1:00 Kolansky, Jeremy
1:15 Moberley, Andrew K.
1:30 Toulouse, Michael W.
1:45 Guthrie, Daniel F.
2:15 Mills, Ashleigh M.
2:30 Crump, Nicholas A.
2:45 Price, Dennis M.
3:00 Cao, Vincent M.
3:15 LePire, Steven D.
3:30 Simingalam, Sina
Hall effect
Band-gap theory of Solids
Mercury