Introduction to the experiments of Physics

407

Franck-Hertz experiment: confirmation of quantized atomic energy levels

Franck-Hertz

1st evidence: Spectrum from a low-pressure mercury lamp

Sketch of Franck-Hertz Apparatus

+

Franck-Hertz

accelerating voltage

Heated cathodeproduces electrons

after Krane

Positively charged grid accelerates electrons

Current from collectormeasured as a function of accelerating voltage.

Collecting plate is slightlynegative compared to grid –so only those electrons above an energy threshold will reach it.

Voltage between peaks corresponds to excitation energy

4.9 V

Franck-Hertz

                                                                                               

    

Hall effect

Hall effect with negative charge carriers

+

http://hyperphysics.phy-astr.gsu.edu

Direction of conventional Electric current

Fe = electric force from charge buildup

Fm = magnetic force on negative charge carriers

Hall effect in semiconductors

Dominated by negative carriers. Dominated by positive carriers.

Hall effect

Johnson Noise

+ 0 Vrms??

Cause:Thermal motion

Johnson noise

Johnson Noise:way to measure Boltzmann’s constant

Johnson noise

JB Johnson, Physical Review 32 (1928) 97

Brownian motion:more evidence for thermal motion

Brownian motion

Perrin’s Atoms Nakroshis et al. AJP 71 (2003) 568

State space of a dynamical systemChaos

James P. Crutchfield, J. Doyne Farmer, Norman H. Packard, and Robert S. Shaw SCIENTIFIC AMERICAN DECEMBER, 1986 VOL. 254 NO. 12, 46-57.

IDEAL FRICTION

ChaosChaos

Chaotic behavioris characterized by divergence of nearby trajectories.

Lyapunov exponent is a measure of this divergence.

10,000 red dots

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

2 slit interference, one photon

http://www.blacklightpower.com/theory/DoubleSlit/

2 slit interference, one photon

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

Faraday effect

The Zeeman effectZeeman effect

The Zeeman effect: Mercury energy levelsZeeman effect

Fabry-Perot distinguishes wavelengths

Zeeman effect

Optical Pumping

F=2

F=1

F=2

F=1

B increases

5P1/2

5S1/2

Hyperfine

mF

2

-2-1 01

light795 nm

462 MHz

Optical pumping

Nuclear magnetic resonance

NMR

B-field

Electron Spin Resonance (ESR)

Organic salt, DPPH

Microwaves

Microwaves

www.microwaves101.com

Compton scattering: light as a particle

Muons are produced in cosmic raysMuon Lifetime

www.lanl.gov

Properties of the Leptons

Particle SymbolAnti-particle

Rest massMeV/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

Muon Lifetime

http://alpha.sci.osaka-cu.ac.jp/grapes3

plastic scintillator photo-multiplier tube

Muon Lifetime

www.prestoncoll.ac.uk

Typical muon-electron pulses from the photomultiplier tube

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

Cassini approaches Saturn (Artist's impression: NASA)

Langmuir probe on Cassini/Huygens (Photo: IRF Uppsala)

Plasma

Cavendish experiment:measure of G, gravitational constant

http://fas.harvard.edu

2 equilibrium positions double the accuracy

Experiment 1 order12:30 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

Band-gap theory of SolidsHall effect

Mercury