2005 PNACP Conference Abstracts

The final project in Whitworth's electronics class requires students to construct a robot containing custom transducers interfaced to a LEGO RCX. The RCX is an 8-bit, 16-MHz computer with 32 kB of RAM, an IR transmitter and receiver, three voltage input ports, and three voltage output ports. This five-week-long project gives students an opportunity to creatively apply the knowledge of analog electronics that they acquired in the highly structured labs completed during the first two-thirds of the course. This talk will describe our experience with this project and the rewards (and challenges) that come from designing an electronics course to accommodate such an extended project.

Favorite Demonstrations After 25 Years of Using Computers in Physics Teaching

I started using a computer for demonstrations when I was a high-school physics teacher in the 1970's. In those days, the computer offered a way to do photogate timing and display the results so the whole class could see them. It also allowed me to display readings from analog sensors on a screen that was bigger than an oscilloscope. The computer soon brought several other advantages:

- Because the results could be quickly graphed, the demonstration could be repeated with different conditions.

- Teachers could demonstrate physical interactions which took place very quickly, such as collisions, or very slowly, such as thermodynamics experiments.

- Improved analysis tools allowed displays of FFTs, histograms, statistics, and curve fits.

Now photos and videos can be integrated into demonstrations, opening up new possibilities. In this talk, I will show some of my favorite demonstrations, old and new.

The Kelvin generator is an electrostatic induction device invented by Lord Kelvin (1824-1907). The operation is amazingly simple. Two small jets of water pass through two insulated metal cylinders into two insulated metal cans, which are cross-connected with the cylinders. A small charge on one of the cylinders induces a charge of the opposite sign in the jet of water passing through it. This charge is carried to the can below. It then travels to the other cylinder, giving it a charge opposite that of the first cylinder. A large potential difference quickly develops between the cans. This is limited since the charged water drops are repelled by the cans of like charge. The energy stored is quite large enough to cause a small neon bulb to flash repeatedly. The generator will be demonstrated, a circuit model will be presented, and photographs showing the drops spiraling under the electrostatic force will be shown.

The December 26, 2004 Indian Ocean tsunami that claimed over 200,000 lives and devastated many Indian Ocean shorelines is the best-documented major natural disaster in human history. But what is the geophysics behind the newspaper headlines and the startling video images? The basic physics of tsunami has been known for decades and we have reasonable understanding of tsunami wave dynamics and travel times in the open ocean. However, we are not yet able to predict in real time whether a tsunami will result from a particular earthquake. The tsunami record, hazards, and emergency preparedness of the Pacific Northwest will be reviewed in the light of lessons learned from the Indian Ocean tsunami.

Einstein: The Sage of Princeton versus the Scientist as a Young Man

There is a striking difference between the methodology of the young Einstein and that of the old. I argue that Einstein¹s switch in the late 1910s from a moderate empiricism to an extreme rationalism should at least in part be understood against the background of his crushing personal and political experiences during the war years in Berlin. As a result of these experiences, Einstein started to put into practice what, drawing on Schopenhauer, he had preached for years, namely to use science as his means of escaping from "the merely personal." Whatever the exact sources of Einstein¹s about-face, the older man has left us with a highly misleading picture of how the younger man achieved the successes that we still celebrate today. This has had a harmful influence on theoretical physics. If the young Einstein¹s successes are any guide as to how successful theoretical physics is done, close adherence to general features of the empirical data is much more and mathematical elegance is much less important than the old Einstein wanted us to believe.

The year 2005 is the centennial of Einstein's miracle year, 1905, in which he published five of the most important papers ever published in physics. One of them won him the Nobel Prize, but surprisingly it was not the most important of them. Einstein is an inspiration to us all because he underwent tremendous turmoil and had numerous personal problems in the years before 1905, and yet he went on to become the greatest scientist of all time. I will talk about his turmoil, his miracle year, and his even greater contribution to physics that came in 1915, namely general relativity.

As part of our assessment efforts, we have been giving a survey to students in our introductory science courses. The survey looks at knowledge of science and attitudes toward science. This talk will be a brief summary of what we have learned.

A pair of microscope slides, separated by a variable layer of air, readily reveals thin-film interference. And as noted in Problem 4.72 from the 4^th edition of Hecht’s Optics, transmittance is significantly reduced—even at normal incidence—as a beam of light encounters successive air-glass interfaces associated with a stack of slides. In addition, the increased optical path length, associated with light that passes through a glass slide (as compared with air) is noted in a shift of the fringes observed in two-slit interference. An illustration of coherence length also is presented.

What is the purpose of a lecture demonstration? General guidelines and principles for presenting memorable demonstrations, whatever their purpose, will be discussed. What makes a demonstration an effective teaching tool? Methods for maximizing the pedagogical value of demonstrations will be reviewed.

Tops, Rattlebacks and Tippe Tops

When I teach advanced mechanics I look at the motions of three top-like objects: a rattleback, a tippe-top, and a spinning coin on an incline. These are different from a typical top and have some surprising motions.

Most physics departments probably have a balancing bird used for demonstrations on equilibrium, sitting on the shelf. I'll show how I think this same bird has much to offer in the way of understanding rotational motion, torques, and angular momentum.

I am in my 20th year of coordinating the universe around us in such a way as to demonstrate in action the nature of a phenomenon being discussed in theory. The physics always works. It is the universe that just does not fully cooperate from time to time and shows us something else. The aspects, history and need of lecture demonstrations will be discussed along with some emphasis of what one could possibly do for The World Year of Physics 2005.

Demonstrating Chaos with Sprott Circuits

Undergraduate physics students are typically introduced to the phenomena associated with chaos through demonstrations and activities with mathematical models, for instance the well-known logistic map^¹. Widely available, powerful computational technology has made mathematical modeling of chaos easily accessible and a popular topic in the physics curriculum, but in the context of teaching physics as an experimental science it should be important for us to engage students working toward an understanding of chaos early on in the consideration, examination, investigation and understanding of actual physical systems displaying chaos. Sprott, et.al.,^² have reported on a class of chaotic systems that can be simply constructed from discrete electronic components, the most complicated of which is an operational amplifier, and that can be modeled with simple differential equations. The electronic circuit realizations of these systems can be built, manipulated, investigated and understood by students with only a very modest background in the techniques of laboratory electronics. We have successfully used some of these systems as hands on demonstrations and laboratory exercises in chaos for undergraduate physics students, demonstrating and investigating such phenomena in chaos as time series, phase space, bifurcations, and Lorenz maps. We will present our findings and recommendations for using these systems as demonstrations and laboratory exercises for introducing chaos. We will also make a chaotic Sprott circuit demonstration available for meeting participants to examine and investigate during meeting breaks.

2 Sprott, J. C. (2000), "Simple chaotic systems and circuits," American Journal of Physics 68(8): 758-763 and Kiers, K., D. Schmidt, et al. (2004), "Precision measurements of a simple chaotic circuit," American Journal of Physics 72(4): 503-509.

The Do's and Don'ts of Demos

Dean Hudek, Director of Instructional Labs & Demonstrations

Brown University

Demonstrations are an important part of learning physics. An effective demonstration can clarify, cause discussion, or maybe
most importantly generate enthusiasm. Using experience gleaned from 20 years experience with lecture demonstrations, 15 years involvement with PIRA, and just recently 2 years as Chair of the AAPT's Committee on Apparatus, this talk will explore demonstration techniques that have proven to be effective as well as those that have proven to be ineffective.

The 1-D Step in Two Dimensions - Where Quantum Mechanics, Classical Mechanics, and Classical Optics Agree.

Brian Houser

Eastern Washington University

In a one-dimensional calculation, classical mechanics and quantum mechanics agree on the probability for reflection when particles are incident on a stepwise increase in potential energy AND the particle's energy is less than the step height. They disagree when the particle energy is greater than the step height. A two-dimensional extension allows for oblique incidence on a 1-D step, giving rise to total reflection even when the particle energy is greater than the step height, provided the incident angle is above a critical angle. The expression for the critical angle is the same in both quantum and classical mechanics, and takes on the same form as the familiar optical counterpart.

Psi meets Y: Methods from the “particle-in-a-box” problem applied in forensic genetics.

Dennis Garvey

Gonzaga University

The methods that we learn in our physics courses can turn out to be useful in a surprisingly wide range of fields. I’ll discuss an interesting example of one of these “physicist-at-large” problems in the field of forensic genetics.

The Y chromosome is the part of the human genome that determines maleness. Forensic geneticists are learning how to distinguish one man from another based on the patterns seen in their Y chromosomes. It turns out that we can model all the Y chromosome patterns seen in a population in the same manner that we model particles in a “tiny” N dimensional box. I’ll begin with a review of the particle-in-a-box problem. Then I’ll bring you up to date on what kind of DNA patterns the CSI folks are looking for these days. We’ll end by using our understanding of the particle-in-a-box problem to discuss Y the last ice age made the job of forensic geneticists more difficult.