Note: Some of the online lecture notes and WWW resources are in PDF (Adobe
Acrobat) format. You can obtain a free Adobe Acrobat Reader here
- Michelson-Morley Experiment (Adobe Acrobat PDF) from W. H. Freeman publishers.
- Doppler Effect animation "applet" - control the speed of the source and compare classical/relativistic results. Here is a more whimsical example.
- The
Twin NON-Paradox - restates the problem and makes the ``paradox''
trivial to resolve!
This is how we would measure a
cartwheel in the few moments it passes by us at 87% of of the speed of
light. At axle height, the wheel appears Lorentz-contracted by a factor
of 2 along the direction of motion. The bottom of the cartwheel, where it
touches the road, is not moving, and is not Lorentz-contracted. You might
think that the top of the cartwheel would have to move faster than the speed
of light to overtake the axle moving at 87% of the speed of light; but of
course it can't (remember how to add velocities!). The cartwheel is also an example of the impossibility of completely rigid bodies in special relativity. The rim is Lorentz-contracted, but the spokes have their full length when vertical - they must bend and compress, otherwise they could be used to transmit a signal faster than the speed of light.
- Streetcar Movie (0.5Mbyte, mpeg) If the speed of light were only 10mph, this is how we would see (note NOT measure) a passing streetcar moving at 0.86c. In addition to the real effects of Lorentz contraction, time dilation and Doppler shifts, what we see also depends on the travel time for the light rays to reach us, adding an "apparent" distortion to our view. What a passenger riding on the streetcar sees (1.5Mbyte mpeg)
Lectures 9, 10 - refer to the Reading below- Reading:
- Krane Chapter 3, in the following order:
Intensity of electromagnetic waves, X-ray diffraction (Section 3.1),
Blackbody radiation (section 3.3), Photoelectric Effect (Section 3.2),
Compton scattering (section 3.4).
You may omit: Young's double-slit experiment, Bremsstrahlung, Pair Production. - WWW resources:
-
Blackbody
Radiation Laws - excellent summary of the basics we covered in lectures,
with graphics, and derivations of Stefan's Law and Wien's Law. (Don't bother
with the fancy VRML model).
Blackbody Java tool. If you can get this to work on your browser, you may be able to plot the Blackbody Radiance as a function of wavelength for a variety of temperatures, and look at the "color" of the resulting spectrum.
Or, try this version from the University of Kentucky (select "NORM=no" to see how total power changes as temperature4).The most precise blackbody in nature is the whole universe, filled with blackbody radiation at a temperature of 2.7 K. See how well the curve fits the data in this brief Cosmology Tutorial by Ned Wright at UCLA.
Also read Krane section 3.6 on "What is a photon?" Here is what Albert Einstein had to say: ``All the fifty years of conscious brooding have brought me no closer to the answer to the question, "what are light quanta?" Of course today every rascal thinks he knows the answer, but he is deluding himself.''
Here are two excellent animations of alpha particle scattering for Thomson's ``Plum Pudding'' and Rutherford's nuclear model of the atom. Both animations have links to a well-written description of Geiger & Marsden's experiment and later developments, leading to the birth of a new field - nuclear physics.
For an entertaining (if slightly cheesy) description of the Bohr atom, with some animations, visit The Quantum Zone, part of the Physics 2000 educational project.
Here is a slightly more informative description of the Bohr Model, with some useful links.
Some examples of atomic emission lines arising from quantized energy level transitions:
For an alternative, easy-going introduction to this material, with some nice animations, discover the Wave Nature of Matter at the Physics 2000 WWW site.
An excellent explanation of the connection between waves, particles, and probability is this article on the Two-Slit Interference Pattern (courtesy of W.H. Freeman publishers).
See also the entertaining Physics 2000 virtual experiment allows you to simulate a two-slit experiment using animated plugins. Cute cartoons also.
Finally, here is a Heisenberg Uncertainty Principle applet which demonstrates that the more you confine a wave packet's position, the more wavenumber components you need to include.
GroupVelocity applet and description.
Here is an Mpeg movie of a wave-packet dispersing as it travels.
Superposition of opposing sine waves - this applet shows clearly that a standing wave results in the special case when two equal and opposing waves interfere.
Fourier Synthesis - create your own wave-forms and listen to them!
Quantum Mechanical Scattering applet. Solves the Schrodinger equation in real time for a wave packet incident on a variety of potentials. Click "Stop" to change the form of the potential (a barrier, a well, or "none"), then "Restart".
Time Dependent Schrodinger equation tool. Draw your own potential barriers with the mouse, and watch a plane wave or a wave-packet evolve as it interacts with it.
Mpeg movie of a wave-packet tunneling through a potential barrier. SuperWave - a free program Windows 95, allows you to view time evolution of wavefunctions on your PC.
Scanning Tunneling Microscope (STM) WWW site from IBM.
If you have access to a Mac, download the excellent Atom in a Box software which allows you to animate 3-d views of the electron orbitals in an H atom. Even if you do not have a Mac, the WWW page offers excellent animations in any case.