14 October 1997: Jane Shields [Chicago SDA Academy]
She showed using the Lite Brite box with colored pegs that are plugged into a grid on the front with a light source behind for a presentation geared at elementary school science classes.
She would break the students up into groups. One would determine the # of Electrons, and the Protons, in an atom from the periodic table. The plug-in pegs were put at the appropriate position. She used Helium [He] for a demonstration because it is a simple configuration.
27 October 1998: Magdalena Lilisa [Good Counsel HS]
She talked about the size and internal structure of atoms. She demonstrated a method of indirect investigation, using Bags filled with play-dough to simulate particles and learning the size and shape of the contents indirectly by using a needle or something passing through the object.
J J Thomson discovered the electron in 1898 [http://www.aip.org/history/electron/jjhome.htm]
and developed a "plum pudding" model of the atom. According to Lee
Slick [Morgan Park HS], the stuff is marginally edible! This atomic
model was disproved by the experiments of Geiger and Marsden [circa
1908] of alpha particles from gold foil. The occurrence and
understanding of "hard scattering" events [only 1/10000 of the total
number of scatterings] led to development of the currently accepted
Rutherford Nuclear Atomic Model, in which most of the mass of the atom
lies inside a tiny nucleus.
Somebody [?]showed us several line pictures that changed their apparent proportions when rotated For a discussion of the various types of optical illusions, see the website http://library.thinkquest.org/J0110336/types.htm
02 March 1999: Carol Zimmerman [Lane Tech HS Physics]
She brought in 2 newspaper articles.
Porter Johnson commented about Whistlers that appeared on the radio frequencies, and these were alleged to come from static discharges [lightning] occurring in the southern hemisphere and heard in the northern as a change is frequency due the distortions. Being helical polarization each polarization travels differently, thus the whistler-change in time causing change in frequency. Here is an excerpt from the following source: http://plasma.udw.ac.za/plasma/tut/tut.html
Also see http://www.auroralchorus.com/natradio.htm.
Whistlers are a common phenomenon in our own magnetosphere. They may be excited, for example, when electromagnetic energy from a lightning strike enters a magnetic field line duct (a process, which is more efficient near the magnetic poles). Such electromagnetic energy can be guided along closed magnetic field lines though the enhanced ionization usually present near such magnetic field ducts. The wave travels along the field line and can be observed at the opposite pole (conjugate point). Because the wave is highly dispersive (see above) different frequencies arrive at the conjugate point at different times and, using a radio receiver, a descending glide tone can be heard for each lightning strike occurring in the opposite hemisphere. Whistlers also occur widely in the plasmasphere, magnetosheath and terrestrial foreshock, for example.
10 December 2002: Larry Alofs [Kenwood Academy, Physics
] How do
Larry called our attention to the following website: [http://www.howstuffworks.com/question631.htm]
25 February 2003: Earl Zwicker passed around an article, Manipulating Nanoparticles [http://focus.aps.org/story/v11/st6], which concerned laser-produced standing waves used as optical tweezers to manipulate micron-sized particles.
06 May 2003: Earl Zwiclkr called attention to a Focus Story, How to Grab an Atom, on the American Physical Society webpage: http://focus.aps.org/story/v11/st19.
12 April 2005: Earl Zwicker called attention to a recent article In Still Waters, Protons Run Deep [http://focus.aps.org/story/v15/st12]. The article describes the fact that, at high temperatures and under extreme pressures, hydrogen nuclei in water can roam and conduct electricity, as electrons do in a metal. The discovery could help explain the presence of magnetic fields in the planets Neptune and Uranus, which may contain large amounts of "hot ice" in their depths.
Arlyn Van Ek mentioned an enthralling film "The Strange Case of Cosmic Rays", which is appropriate for high school science students. This film was prepared many years ago by Bell Telephone Films, and a DVD version exists today. Arlyn also mentioned a magnetic array that may be used to illustrate the expansion of H20 in going from the liquid to the solid phase.
12 April 2005: Fred J Schaal [Lane Tech HS,
A particular question about a particle
Fred made reference to the book Parallel Worlds by Michio Kaku, which describes neutron stars. Kaku explains that in neutron stars, gravitational attraction prevents the neutrons from repelling one another. Fred's question is: Why would neutrons repel one another in the first place?
Porter Johnson explained that, in ordinary nuclei, because of the strong force neutrons and protons attract one another at distances of order 1 Fermi = 1 femto-meter = 10-15 meters. However, both neutrons and protons (as well as electrons) are Fermions (spin 1/2 particles), and no two of them can be in the same state. The Pauli Exclusion Principle requires that neutrons and protons must occupy states of progressively higher energy in nuclei. Protons repel one another with the long-range Coulomb force. Consequently, stable heavy nuclei become neutron-rich. For example Uranium 238 has 92 protons and 146 neutrons. Big nuclei eventually become unstable, even when they are neutron-rich, because of the Coulomb repulsion of protons, in agreement with the Pauli principle, the heaviest known nucleus containing about 118 protons. It has long been postulated that extremely neutron-rich massive objects could become stable. These "neutron stars" are predicted to have one solar mass and a radius of about 10 km, corresponding to a density of 1018 kg/m3 --- the density of heavy nuclei. There is overwhelming evidence for the existence of such neutron stars, which are called pulsars since they emit sweeping searchlight beams (seen as pulses) of electromagnetic radiation.
Good question, Fred!
12 April 2005: Charlotte Wood-Harrington [Brooks HS,
Geek of the Week
Charlotte passed around the book Teaching Introductory Physics by Arnold Arons [Wiley 1997; ISBN 0-471-13702-3], which contained some invaluable advice: http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471137073.html.
Charlotte is going to work on the D0 detector at Fermilab this summer, as a result of her involvement with Quark Net. She has a cosmic ray detection system in her classroom, and there is a similar one at Walter Payton HS. The idea is to put them at various locations around the city, possibly including Millenium Park, so that Extensive Air Showers of cosmic rays can be monitored. Primary cosmic rays strike the upper atmosphere of the earth (say, about ten kilometers above the ground), and produce a spray of secondary particles, mostly muons. These muons may travel to the earth's surface, and be detected. If the primary cosmic ray is sufficiently energetic, the air shower may spread over the entire city at ground level. Very exciting stuff --- and in her own classroom!
In connection with a vivid description of reveries involving a midlife crisis, Charlotte mentioned that she had recently obtained a Toyota Prius™ automobile with a hybrid engine. It is a joy to drive, and she gets 48 miles per gallon. The gasoline engine is started with a small auxiliary battery, which becomes discharged because of power requirements, when the car is not driven for a period of about two weeks. A trickle charger would maintain it.
26 April 2005: Earl Zwicker called attention to the article Controlling Heat Flow with a Magnet, which is described on the Physical Review Focus web page: http://focus.aps.org/story/v15/st14.
26 April 2005: Fred Schaal [Lane Tech HS,
Follow-up Questions on Book by Michio Kaku
How is the Einstein-Podolsky-Rosen (EPR) paradox resolved in a manner consistent with the requirements of relativity?
The essence of the EPR paradox involves the spontaneous decay of a particle at rest into two particles. The standard pedagogical answer involves the neutral pi meson p0, which decays spontaneously into two photons (g1, g2) in about 10-15 seconds: p0 ® g1 + g2 . The p0 has spin (intrinsic angular momentum) zero, whereas the two photons are spin-one particles. In other words, the total angular momentum of the system in the rest frame starts at zero, and it must remain zero -- in the absence of interactions with the external world. Each of the gamma rays has an energy of about 70 MeV -- which is easily detectable. Suppose that each one travels freely for years before being detected by the LGM (little green men) on distant planets circulating around distant stars. Suppose that the LGM on one of the planets measure the photon spin (left or right circular polarization). They then know the spin that the LGM on the other planet would simultaneously measure. But, relativity requires that information cannot travel faster than the speed of light, and it doesn't in this case, even though it may appear so..
Einstein was, in effect, attacking Bohr and Quantum Theory, and not his theories of relativity, through such a Gedanken Experiment. Modern developments suggest the use of this "entanglement" of the states of decay products to make a quantum telegraph, which would transmit signals that can only be received by one observer, and would then be erased.