Conference Workshops
This is a list of workshops planned for the BFY conference. It is a partial list as we continue to develop the conference. If you have a suggestion for a possible workshop, please contact us.
 Using a Chaotic Pendulum to turn Sophomores into Experimentalists
Marty Johnston, Univ. of St. Thomas
Quantifying the behavior of a nonlinear pendulum provides the setting for a semester long introduction to experimental methods. Students learn electronics, LabVIEW, data acquisition, and numerical analysis as they build stepper motor controllers, hardware timed data acquisition systems, and analysis software used to study the rich behavior of a chaotic pendulum.
The course is designed to build both the skills and confidence that students need to take on the ill-defined and difficult problems that they will see in the future. The first two thirds of the course is devoted to building the apparatus and controls, the data collection system, and writing the basic analysis software displaying Poincare' sections and bifurcation diagrams. The physics, technical topics and mathematical tools are presented as the topics become relevant. Homework problems and written work is assigned and tested on throughout the semester. Students work at their own stations but discuss problems with their peers in a collaborative environment. During the last third of the course students conduct individual explorations of different aspects of the chaotic pendulum. These investigations vary from measurements of Lyapunov exponents and correlation dimensions, to building FPGA stepper motor controllers, to studying chaotic magnetic dipole-dipole interaction. The semester concludes with a poster session where students present what they have been working on.
The apparatus consists of a pendulum operating in a variable magnetic potential. Driving torque is controlled by eddy forces, monitored by hall sensors and modulated by a stepper motor. Optical sensors provide information about position and driving phase. The system is relatively inexpensive which allows an entire course to be equipped at a reasonable cost. In this workshop I will introduce the hardware and software used in the course and discuss how they are used achieve our educational goals for the course.
Statistical/Nonlinear Physics with Subwoofers
David Bailey, Univ. of Toronto
The least expensive experiment in the University of Toronto Advanced Physics Lab has one of the largest phase spaces for student exploration. We originally set out to just develop an experiment to study the unknotting and entropy of chains, but soon realized even more fun is possible with a subwoofer, an amplifier, and a frequency generator. In addition to the physics of chains, which are models for polymers, DNA, and other interesting biomolecules, versions of the system can be used to observe nonlinear waves in liquids and particulates, to study chaotic bouncing balls, and to try to create experimental models of fluids and crystallization.
Workshop participants will play with two different systems: one has a basic subwoofer that is capable of knotting and bouncing ball experiments, and one with a modified subwoofer that can be used for more varied explorations. A picture of the latter system can be found at http://www.physics.utoronto.ca/~phy326/knot/index.htm, along with more information on our basic chain experiment. Information on a Faraday waves experiment using a more powerful and linear shaker can found at http://www.physics.utoronto.ca/~phy326/far/index.htm.
The basic experiment only requires a stopwatch and notebook for data acquisition, and basic fitting software for analysis, but the workshop may also demonstrate Python/ vPython video, analysis, and simulation tools that are under development.
Synchronization and Encryption with a Pair of Simple Chaotic Circuits
Ken Kiers, Taylor University
In recent years, students in Taylor University's Physics Capstone Course have built pairs of nearly identical chaotic circuits that they have used to encrypt, and subsequently decrypt, a signal. These circuits can be constructed using inexpensive parts and can also be modeled very accurately using relatively simple differential equations. Students have found the construction and analysis of these systems to be technically challenging, yet, ultimately, very rewarding. Two methods of encryption have been studied to date; both methods will be demonstrated in this workshop. In the first approach, a digital potentiometer in one of the chaotic circuits is switched back and forth between two settings (corresponding to "ones" and "zeros") in such a way that a binary data stream is encrypted within the chaotic output of the circuit. The other circuit is used to decrypt this data stream. In the second approach, a small analog signal is added to the chaotic output of the first circuit, and is then extracted by the second circuit. In both approaches, the decryption of the signal relies on the fact that the second circuit is able to synchronize its output to the output of the first circuit if the two circuits are identical to each other. Changing the value of one of the resistors in the first circuit (as in the first approach), or adding a spurious signal to its output (as in the second approach), causes the second circuit to be unable to synchronize with the first. In both cases, comparison of the output of the second circuit to that of the first allows for the recovery of the original signal.
Reference:
Ken Kiers, Dory Schmidt and J.C. Sprott, "Precision Measurements of a Simple Chaotic Circuit," Am. J. Phys. 72, pp. 503-509, 2004.
Fundamentals of low-noise electrical measurements: Ground loops, interference, shielding, etc.
Walter Smith, Haverford College
In this workshop, participants will run through the highlights of a series of labs that teach students about amplifier noise, Johnson/Nyquist noise, capacitively- and inductively-coupled interference, and ground loops. Students learn both about the origins of these usually undesired signals, and how to minimize them. The labs require a low-noise amplifier such as a Stanford Research Systems SR560. Optionally, the students can instead design and build their own amplifiers, if time permits, based either on op amps or on instrumentation amplifier integrated circuits. In a culminating exercise, students measure the Johnson/Nyquist noise of a resistor at liquid nitrogen temperature. Workshop participants will be furnished with complete lab write-ups including conceptual questions for the students, complete lecture notes, supporting problem sets and solutions, and sample exam questions and solutions.
Real-world projects for digital & analog electronics courses
Sean Bentley, Adelphi University
With the limited exposure most physics undergraduates get to circuitry, the pieces can often seem disconnected with little tie to real-world applications. To overcome this problem, it is important to expose these students to projects that bring together many of the concepts from the semester. In this workshop, we will explore two examples of application-based semester projects I use in my courses. These include a real-time clock programmed in VHDL on an FPGA educational board for digital circuits, and an AM radio built from discrete components for analog circuits.
Rather than giving the students explicit instructions on the designs, each is asked to build their designs from pieces they have learned throughout the semester. To avoid students just taking a design from the web that they don't understand, when they demonstrate their working designs, they must be able to explain what each section does. Upon completing such projects, the students not only feel a sense of accomplishment, but truly appreciate the importance and connection of many topics learned.
Arduino: PID-controlled thermostat
Sean Robinson, MIT
This workshop will show a simple application of Arduino microcontrollers to solving a common Advanced Lab apparatus problem: regulating the temperature of an oven via modulating the current supply to its resistive heating elements using a PID-controlled feedback algorithm. Consistent with the experience of the presenter, this workshop will be given from the perspective of starting with zero knowledge of Arduino design or programming, and proceeding to a working device without ever becoming and expert.
Teaching with Arduino
Andy Dawes, Pacific University
A hands-on introduction to the Arduino programmable circuit board. The Arduino is a small self-contained micro controller platform that can be easily integrated into analog and digital electronics projects. Programmed in C++ and connected to a computer via USB, the Arduino eliminates many of the traditional hurdles that prevented practical micro controller use in the classroom setting.
You will learn how the Arduino works and how to integrate it with your curriculum on many levels. Arduino can fit in anywhere, from a first-year unit on electronics to an upper-division electronics course and senior research projects. If you are new to Arduino or new to teaching with Arduino, this is the place to start. There are several other Arudino workshops at BFY where you will be able to extend what you learn here.
Arduino as a "gateway drug"
Eric Ayars, CSU-Chico
The Arduino can do a lot, but sometimes you don't need to do that much. In many cases, it's simpler (and more economical) to use a smaller microcontroller such as the ATtiny series rather than the full Arduino platform. Fortunately, the same user-friendly Arduino IDE can be used to program these smaller microcontrollers: in fact, you can use the Arduino as the programmer. In this short workshop I'll demonstrate how to do this, and show some of the uses we've found for ATtiny microcontrollers in our upper-division labs.
Using Cypress Programmable System on a Chip as part of a electronic instrumentation course
Mark Masters, Indiana Univ-Purdue Univ. Fort Wayne
The Cypress PSoC is different from a traditional microcontroller because it incorporates analog circuitry such as op-amps on chip. These analog elements are defined through software. The inclusion of these analog components makes building instrumentation somewhat simpler because of the greatly reduced chip count. We extensively use PSoC's in our electronics instrumentation course in which students are expected to design, test, and build an electronic instrument and use that instrument to perform an investigation.
In this workshop we will go through the basics of creating a program for the PSoC. Workshop attendees will use a PSoC to build a simple electronic instrument (there will be several different options) and hopefully test it.
Introduction to FPGA's
Matthew Vonk, Univ. of Wisconsin - River Falls
Field Programmable Gate Arrays (FPGA's) are user configurable integrated circuits that can be designed to perform specific tasks with true parallelism, unlike microprocessors which operate sequentially. Their flexibility, ease of use, and relatively low cost has made them increasingly popular in a wide variety of applications.
This workshop would show attendees how to use the Xilinx ISE development software (a combined smart-editor, simulator, and synthesizer which is available for free on the Xilinx website) to interface with Digilent FPGA-boards. The boards are extremely user friendly, with lots of built-in inputs and outputs, and are also very reasonably priced.
The workshop will show users the basics of writing, compiling, and instantiating code and will step attendees through several practical applications.
FPGA Coincidence Module
David Branning, Trinity College
Many quantum optics experiments are making their way into the undergraduate laboratory, motivated by their effectiveness at demonstrating fundamental features of quantum mechanics. These experiments usually involve the detection of two or more photons simultaneously at different detectors, called "coincidence counting." We have developed a small, inexpensive, flexible, and intuitive coincidence-counting module to be used in conjunction with single-photon detectors, that anyone can build. In this workshop, we will discuss how to assemble and operate the module, and outline some of its uses when paired with a parametric downconversion light source.
Single Photon Labs
Barbara Hoeling, CSU-Pomona
Quantum optics experiments are becoming more and more popular in the advanced student laboratory. With a blue diode laser beam impinging on an optically nonlinear crystal (beta barium borate BBO), pairs of entangled photons are created. With this heralded single photon source, quantum optics experiments such as anti-coincidence, single photon interference, and tests of local realism can be performed. Essential pieces of equipment for these experiments are single photon detectors, avalanche photodiodes (APDs) operated in Geiger mode that are capable of detecting individual photons. In most advanced student labs, the commercially available, fiber-coupled single photon counting modules by Perkin-Elmer/Excelitas are used. We are presenting single photon detectors developed at the University of Erlangen, Germany, which use either the APDs by Perkin-Elmer/Excelitas or by LaserComponents together with "home-made" electronics. We discuss their performance in comparison to the Excelitas product and their potential advantages in a free-space set-up.
Temperature Dependent Lifetime Measurements of Fluorescence from a Phosphor
Jim Parks, University of Tennessee
This laboratory activity exploits the very efficient fluorescence of atoms that are constituents of solid state phosphor materials. Learning and working with fluorescence the student learns concepts and experimental techniques not just applicable to atomic physics but to a wide range of disciplines including chemistry and the life sciences. The objectives of this experiment are: (1) to study and investigate the principles of atomic lifetimes, (2) to learn experimental techniques for measuring lifetimes, (3) to study and investigate the energy pathways in a solid that fluoresces when excited, (4) to measure and analyze the temperature dependence of fluorescent light lifetimes (of a particular wavelength) emitted from a phosphor material excited with a nitrogen laser, LED, or other energy source, (5) to learn computer-based data acquisition and analysis procedures for measuring temperature dependent lifetimes, and (6) to learn a practical application for this technique. The basic apparatus can easily be adapted to incorporate other more advanced subjects such as signal processing, signal-to-noise investigations, and optics-based sensing.
1. Department of Physics and Astronomy, 401 Nielsen Physics Building, The University of Tennessee, Knoxville, Tennessee 37996-1200.
2. Sensors and Controls Research Group, Measurement Science and Systems Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN. 37831-6056.
3. Emerging Measurements Company, 9910 Kay Meg Way, Knoxville, TN. 37922.
Tabletop Relativity with the Compton Effect
C.J. Martoff, Temple University
The Compton Effect was shocking enough in its day to warrant award of the Nobel Prize in Physics just five years after its publication in 1922. The effect consists of a scattering of short wavelength electromagnetic radiation (x-rays or gamma rays) by matter, with two important characteristics. The energy of the scattered radiation is lower than that of the incident radiation and varies continuously with the scattering angle; and this energy and its angular variation is independent of the material from which the scatterer is made.
The Compton energy shift was astounding enough. Classically, electromagnetic radiation accelerates charges in matter, causing them to radiate according to Larmor's formula, with the scattered radiation necessarily at the same frequency as the incident radiation. The energy shift can only be understood in a "billiard ball" scattering model of "photons" (light quanta) on electrons, in which case the energy shift arises naturally from the conservation laws.
But there's more to the Compton effect than quantization. For easily accessible gamma ray energies this process leads to rather relativistic electrons, allowing a tabletop experiment to measure the relativistic energy-momentum law. For example, 137- Cs gammas with 661 keV lead to a maximum recoil electron kinetic energy of .466 MeV, corresponding to distinctly relativistic parameter values b = .85 and g = .52. The experimental setup allows us to independently measure the energy of these electrons (from the energy difference of incident and scattered gamma rays), and their momentum (from the difference in incident and scattered gamma ray energies and the formula E = pc, compatible with classical Maxwell/Poynting theory). The point of the experiment is to notice that the experimental results would not conserve energy and momentum if the electron obeyed nonrelativistic E = p2/2m, but rather requires the relativistic relation E2=p2+m2c4. The deviation is not small, amounting to over 40% at the most backward angles.
Compton did not encounter this deviation because the x-ray energies he used were much less than the electron rest mass. Another way to view the result in terms of varying (relativistic) electron mass is given by R. Peterson in his internet document: ftp://www.pasco.com/Support/Documents/English/SN/SN-7901/Spectroscopy.pdf
Optical Spectroscopy/Zeeman Effect
Greg Elliott, University of Puget Sound
The Zeeman effect offers a striking visual demonstration of a quantum system and provides a detailed, multi-faceted corroboration with the theoretical treatment. How can one see the effect and observe the various experimental dependences and not end up believing in quantum mechanics? At the University of Puget Sound the effect is first introduced at the sophomore level in Modern Physics, and then treated in full mathematical detail in senior level Quantum Mechanics. The seniors spend some time observing and quantifying the effect, as one of a few experiments that complement their theoretical studies. Students have also explored the effect in the advanced lab course, and as independent study and summer research projects.
Following an NSF sponsored workshop on advanced lab curricula in the 1990's, we built an Ebert spectrometer to observe and study the Zeeman effect and the fine structure of hydrogen.1 Our instrument has evolved over the years, and now consists of four elements: (1) a discharge source in the field of a permanent magnet, that illuminates an adjustable width slit, (2) an objective mirror (12" diameter f/8), (3) an Echelle grating on a rotary stage, and (4) a ccd camera detector. Working at high order (~20), the Echelle grating gives a resolving power in excess of 500,000 and a resolution of about .01.
A mercury discharge produces several transitions of interest for observing the Zeeman effect.2 The normal effect is observed for the yellow 1D2 1P1 transition at 5790.65 , yielding three lines. The anomalous effect is observed for the blue 3S1 3P1 at 4358.35 (six lines) for the yellow 3D2 1P1 transition at 5769.59 (nine lines) and the green 3S1 3P2 transition at 5460.74 (nine lines). The splittings and the line polarizations yield a quantitative test of the agreement with the predictions given by the Lande g-factor.
For the workshop I will give a brief tour of the instrument, discuss some of the experimental difficulties in its construction and operation, and demonstrate the effect for the mercury (and other) systems.
1. D. Preston and E. Dietz, The Art of Experimental Physics, Wiley 1991.
2. G. Herzberg, Atomic Spectra and Atomic Structure, Dover, 1944.
External cavity diode lasers and iodine spectroscopy
Chad Hoyt, Bethel University
External cavity diode lasers (ECDLs) are common tools in undergraduate and graduate laboratories. One can tune and stabilize inexpensive laser diodes (as will be done here) to be used in contexts such as high precision optical metrology and spectroscopy experiments. Their relative ease-of-use, potential for customization, low price, and large choice of wavelengths make them accessible and interesting parts of undergraduate advanced laboratories.
The apparatus in this workshop will comprise components of a home-built external cavity diode laser system: machined mounts, temperature controller, precision current source, pzt driver for fine tuning, etc. Participants will have the opportunity to align and tune an ECDL at 633 nm. They will also scan the laser frequency for simple absorption spectroscopy in iodine vapor. Versions of this workshop have been offered at the AAPT summer meeting in Portland in 2010 and at an ALPhA Immersion at Bethel University in 2011. Participants will be offered schematics and a parts list for a home-built ECDL system based on a NIST design.
Fresnel and Fraunhofer Diffraction Lab with a Modeling Emphasis
Ben Zwickl and Heather Lewandowski, Univ. of Colorado-Boulder
Every physics lab has a special moment where students, after hours of toil, compare their laboriously collected data with theoretical predictions. At this moment, neat and tidy theoretical predictions are viewed side-by-side with messy and complicated real-world results. How can we make the most of this educational opportunity?
At the University of Colorado Boulder we have partially answered this question by redesigning our senior-level Optics and Modern Physics Lab to emphasize creating, testing, and refining of models, whereby "model" we mean a simplified representation of a more complex system that has predictive power and specified limitations to its validity. By emphasizing modeling, students use the full suite of mathematical and computational tools from their lecture courses to make predictions about the behavior of real-world systems. In the lab, a model-based approach allows for an improved discussion of topics we previously neglected, such as systematic error and understanding various "black box" measurement tools.
A model-based approach can be applied to any experimental setup, but in this workshop we will demonstrate the transformation process from a standard Fraunhofer diffraction lab into a model- based experiment. This change gives students the ability to identify and account for a number of systematic error sources such as non-uniform slit illumination, non-parallel slits, and finite detector width. Students also apply "theoretical" techniques such as Taylor series approximations to predict and test the validity of the Fresnel and Fraunhofer diffraction integrals. In addition, the measurement system, composed of a photodetector with an adjustable size aperture, is modeled to allow students the power to predict both the shape and the magnitude of the observed diffraction pattern - a surprisingly challenging feat. The same setup can be used for other apertures such as a periodic array of slits.
Mathematica is employed for computational modeling. LabVIEW is used in combination with low-cost USB data acquisition devices for quicker data taking. The experimental setup consists of a commercial HeNe laser, amplified photodetector, translation stage, adjustable-width slit, and mounted lenses and mirrors. The equipment can be reused in a variety of optics labs.
At the end of this workshop you will be able to deliver a model-based diffraction lab appropriate for the upper-division level. We will also spend a portion of the workshop discussing how your favorite labs at your institution can be adapted to incorporate aspects of modeling, including systematic error, and a deeper understanding of the experimental apparatus.
Using Spatial Light Modulators to Teach Students Experimental Fourier Optics
Doug Martin, Lawrence University
Shannon O'Leary, Lewis and Clark College
A spatial light modulator (SLM) changes the phase and/or amplitude of light incident on the SLM. The SLMs we use alter the phase of the incident light via an array of 1024x768 9x9 µm pixels. What can these computer-controlled devices be used to do?
We use SLMs to teach students Fourier optics and Fourier transforms, experimentally. As an amplitude modulator (with the addition of polarizers), we use SLMs to create objects within a collimated laser beam. These objects can be imaged with a lens, or, by moving the lens, the Fourier transform of the object can be seen. A particularly simple use of SLMs is in a multiple-slit experiment, where the width of single slits, the spacing between slits, and the total number of slits are dynamically controllable. The single-slit diffraction pattern is a particularly simple Fourier transform; a multi-slit diffraction pattern is a nice application of the Array Theorem.
More interestingly, by placing the SLM in the transform plane of a single lens, the Fourier transform of an arbitrary object can be manipulated; a second lens is used to take the inverse transform and display the modified image. Regularly repeating features of an image can be removed - for example, in one lab, students are given the picture of this kitty in a cage (printed onto a transparency), and asked to remove the cage.
In the workshop, we will use SLMs to:
-perform a multi-slit diffraction experiment, with slit width and spacing changeable onthe fly
-perform 2-D crystal diffraction demonstrations, including quasicrystals
-remove the kitty from the cage using spatial filtering
-create computer generated holograms (along the lines of Thad Walker's Holography Without Photography)
Optical Trapping in Biophysics
Tom Colton, UC-Berkeley
An optical trap, or laser tweezers, is a device used to manipulate objects between about 20 nm and several microns in diameter and to measure piconewton-sized forces on these objects. This scale of operation makes them a useful tool in biophysics to study mechanical properties of cells, organelles within cells, and single molecules involved in movement and force production. An optical trap is a good learning tool in the physics instructional lab because of the insight it gives into mechanical properties of biological structures, but also because of the physical principles of operation and particularly of the techniques used for calibrating position and force. In Berkeley's physics advanced lab course, students spend about 8 afternoons performing several types of calibrations and performing two biophysics experiments. Building and alignment of a trap could be a challenging semester-long project for a small class, though alignment of the Class 3b IR laser requires safety training and close supervision.
An optical trap is essentially a microscope incorporating a trapping laser and position-detection system. Traps can be made either by adding a laser beam path to a conventional microscope or by building the microscope and beam path from standard optical components. We took the latter approach, which makes the optics easier for students to see (though we shield the collimated IR laser beam with lens tubes for safety), and makes it easy to modify. For instance, last summer our students added a second laser to support fluorescence microscopy needed for a single-molecule experiment. Our trap is patterned after one developed for teaching and research at MIT. A somewhat more expensive version is available in kit form from Thorlabs. Our student write-up and information on experiment development is available on our course wiki at http://advancedlab.org. I also recommend the excellent write-up by Sean Robinson on his MIT Physics Junior Lab web site.
In this workshop, we will do the following activities:
-- Practice trapping 1 micron Silica beads.
-- Observe the effect of laser power on the motion of the bead.
-- Record the position of the bead through the quadrant photodiode (QPD).
-- Use the power spectrum of the QPD data and our understanding of Brownian motion to calibrate sensitivity and stiffness of the trap.
-- Examine student-collected data on (1) E. coli flagellar swimming, (2) internal transport of vesicles in live onion cells, and (3) in vitro stall forces measured from single kinesin motor molecules.
Simple Dynamic Light Scattering Apparatus
Bob DeSerio, University of Florida
A HeNe laser beam, incident on a sample of micron-sized spheres suspended in water, scatters into a random pattern of spots of varying size, shape, and intensity. The pattern results from the coherent superposition of the outgoing waves scattered from the spheres and because the spheres are in constant Brownian motion, the pattern changes in time. An avalanche photodiode detector is placed in the pattern to measure the random fluctuations in the light intensity. The autocorrelation function and the power spectrum of the photodiode signal are computed, averaged over time, and fit to predictions based on Brownian motion. The fitting model parameters are then used to determine the diameter of the spheres.
The apparatus will be available for use and complete construction and analysis details will be provided. The geometry of the source, scattering cell and detector will be discussed in relation to the scattering angle dependence of the intensity fluctuations. The circuit for the avalanche photodiode will be provided and the computer hardware and software for collecting and analyzing the signal will be demonstrated. The results for two sphere sizes as a function of scattering angle will be presented.
Simple Experimental setup for demonstrating Surface Plasmon Resonance
Erik Sanchez, Portland State University
Plasmonics has become a very important focus of scientific research. Oftentimes the topic can be difficult to describe to students. The lab demonstrates an optical method for visibly showing the resonance condition. This setup can be easily replicated without the need for typically expensive components. The coating methodology allows for flexibility in coating precision and expense.
Frontiers in Contemporary Physics Education: Gold Nanoparticle Photoabsorption & Quantization of Conductance Experiments
Jan Yarrison-Rice and Khalid Eid, Miami University
This BFY workshop highlights the new pedagogical format of our sophomore Experimental Contemporary Physics course. We strive to provide a strong underlying core of experimental skills in modern topics and, at the same time, encourage students to join faculty research groups. We follow a physics research model using experiments that explore contemporary physical concepts from ongoing faculty research projects. The experimental format shows students "how physics research is actually conducted!" The two experiments we will highlight, 1) Optical characterization of Au nanoparticles, and 2) Quantization of Conductance, were developed as a direct result of the nanoscience and technology research the co-leaders conduct in their own laboratories. Using this basic curricular plan, the course maintains a truly contemporary nature, while providing an introduction to the concepts and instrumentation skills necessary for our students to begin physics research.
1) We explore how surface area, volume and shape change material behavior via optical spectroscopy of Au nanospheres and nanorods (NPs). White light induces a plasmon resonance in the metallic NPs which is measured spectrally. The transmission and scattering spectra of the Au NPs provide a measure how the spectral plasmon resonances reflect the particle morphology. The basic optical setup requires a fiberoptic light source and a reasonably inexpensive spectrometer, as plasmon resonances are quite broad. The excitation of charge carriers in a semiconducting nanowire is introduced next. Finally, both concepts are brought together by describing their application in a plasmon-enhanced nanowire-based biosensor. Students enjoy the visual nature of this experiment and the opportunity to align an optical system.
2) We demonstrate an extremely simple and inexpensive experiment to introduce atomic-scale confinement effects and particle-wave duality. A manual break junction in a gold wire is utilized to explore the quantization of the electrical conductance when the wire width is stretched to the atomic limit. A simple circuit reads the voltage across the break junction via LabView. Just before the wire breaks, the lateral confinement of the conduction electrons causes a step- wise increase in resistance with steps that depend on two fundamental constants of nature divided by an integer. This is due to the wave nature of the electrons that traverse the junction. This experiment is exciting for students because they can measure a complex idea like wave- particle duality with objects that they can "see."
In addition, we discuss how small adjustments make the experiments appropriate for more advanced students.
Granular Materials
Paul Dolan, Northeastern Illinois Univ.
Description coming soon.
Fluid Diagnostics: Compressible Flow and Shock Waves in a Benchtop Blowdown Tunnel
Keith Stein, Bethel University
At Bethel University, fluid mechanics is integrated into the physics curriculum as a required component in the Applied Physics major option. Although the fluid mechanics course is not required for students pursuing other physics major options, most of these students take the course as an elective. Open-ended advanced lab projects are key components of the fluid mechanics course, as is the case in the upper level Optics, Contemporary Optics (i.e. lasers), Electronics and Computer Methods in Physics courses.
In this workshop, we demonstrate the operation of a small supersonic blowdown tunnel (please see figure) that was initially constructed as part of a fall 2010 project in our fluid mechanics course. Following the initial construction and testing of the apparatus, subsequent student research projects have included high-speed video (HSV) shadowgraph imaging and the development of a MATLAB GUI for side-by-side comparisons between simulation and ongoing experiments with the tunnel [1-2]. HSV imaging of the flow in the tunnel was highlighted as a 2011 ALPhA laboratory immersion workshop at Bethel University [3]. Ongoing student project work is supported to further characterize the flow in the tunnel and to assess the 1D isentropic flow assumption for our numerical simulations. Details will be presented on the design, construction, operation and ongoing project objectives with the blowdown tunnel.
1. K. Stein, J. Schommer, and B. Heppner, "Undergraduate Studies on Compressible Flows and Shock Waves," American Physical Society March Meeting 2012, Boston.
2. J. Schommer, K. Stein, and B. Heppner, "Graphical User Interface for Supersonic Flow and Shock Waves in a Converging-Diverging Nozzle," submitted for American Physical Society March Meeting 2012, Boston.
3. "Imaging of Shock Waves in Compressible Flows," Advanced Lab Physics Association (ALPhA) Laboratory Immersion, Bethel University, July 20-22, 2011.
Figure: Preliminary flow imaging with the blowdown tunnel (left); Shadowgraph image sequence of the receding shock wave in the expanding section of the nozzle (right).
New configurations for a hanging chain covered by soap film: Measurement of surface tension from the triangular configuration
Fred Behroozi, Univ. of Northern Iowa
A chain assumes the familiar shape known as a catenary when it hangs loosely from two points in a gravitational field. The derivation of the catenary equation was one of the early triumphs of the newly invented calculus of variations at the end of the 17th century.
We will show that three new and distinct configurations are possible if a soap film covers the area bounded by the catenary as it hangs from a horizontal support rod. We will demonstrate how the chain can assume a concave, triangular, or convex configuration. Furthermore, we will show how the chain can be transformed smoothly from one configuration to another and shall discuss the conditions necessary for each configuration. Not surprisingly, the deciding factor is the strength of the surface tension relative to the gravitational force per unit length normal to the chain.
The conditions under which the chain assumes a perfect triangular configuration is particularly simple and provides an elegant method for measuring the surface tension of the soap film. Naturally the triangular configuration is visually striking but students are more intrigued when they learn that by measuring just one angle of the triangle they can obtain the surface tension of the soap solution.
The convex and concave configurations require more sophisticated analysis and can form the basis of a lab experiment for more advanced students.
F. Behroozi and P.S. Behroozi, "The effect of soap film on a catenary: measurement of surface tension from the triangular configuration", Eur. J. Phys. 32, pp. 1237-1244 (2011).
Video Analysis with Tracker for Advanced Physics Labs
Aaron Titus, High Point university
Video analysis is an inexpensive, easy-to-use technique for measuring the motion of objects with fairly good precision--and it's not just for introductory physics! It allows students to do advanced experiments in classical dynamics such as systems with changing mass, systems studied with Lagrangian dynamics, and systems without analytic solutions such as projectile motion with quadratic drag and spin. It's an excellent technique for labs as well as student projects. In this workshop, participants will learn how to use Tracker which is free, open source video analysis software developed by Doug Brown. Tracker's features include: (1) calibration point pairs that allow you to compensate for panning and zooming of the camera; (2) autotracking of objects; (3) the ability to specify a moving reference frame; (4) automatic calculation and marking of the center of mass of a system; and (5) the ability to solve a differential equation numerically and display the solution on the video. Example experiments include: motion of an American football in a placekick(*), a two-body orbit with a Hooke's law central force(**), and a swinging Atwood's machine(***).
(*_Kevin Sanders at High Point University
(**)Jeff Regester, Greensboro Day School
(***)Leah Ruckle, Davidson College
FPGA Lab Exercise: Using Pulse Width Modulation to Study Analog-to-Digital Converter Properties While Building a Simply Music Player
Kurt Wick, Univ. of Minnesota
During the electronic component of the advanced lab course, students spend one week building a simple music player by programing an FPGA on a Digilent BASYS board. First, they use the FPGA as a digital-to-analog converter (DAC) using a simple Pulse Width Modulation (PWM) technique. This reconfigurable DAC is implemented with a just a few lines of Verilog code and is then used to explore DAC concepts such as resolution and conversion time. Second, an improved PWM technique using a Sigma-Delta algorithm is explored and its application as a voltage-to-frequency converter is discussed. Finally, 8-bit and 16-bit musical data is read from a flash memory and played through a speaker using the Sigma-Delta PWM technique. The workshop will cover the hardware and software used and PWM concepts.
A simple, inexpensive single molecule DNA microscope
Allen Price, Emmanuel College
Techniques for trapping, manipulating and measuring single macromolecules include optical trapping, magnetic tweezers, and flow stretching. These techniques have been used to study DNA replication, RNA folding, protein folding, and gene translation.1,2 These single molecule methods are out of reach for most undergraduates, mainly because of the difficulty of isolating single molecules. Participants in this workshop will learn about how we are making single molecule techniques both simpler and less expensive. Participants will get hands on experience with a microscope that has been used in several senior thesis projects by our students.
Our single molecule DNA microscope uses an upright microscope coupled to a webcam for imaging single DNAs. The DNA molecules are tethered on one end to a glass surface within a microfluidic cell. The DNAs are visualized by tethering paramagnetic microbeads to their free ends. The beads, which can be seen under visual light microscopy, also serve as "handles" for applying forces to the DNA using fluid drag and/or magnets.
We will cover basic webcam video microscopy and microfluidic flow cell construction. We will cover how these two elements can be used to study Brownian motion. Next, we will cover the basics of DNA tethering, including surface functionalization and DNA labeling. These techniques may be new to physicists, and we will discuss the challenges and requirements for successful tethering---the key to a successful single molecule experiment! Our DNA tethering technique takes several hours to complete, so we will not have time to demonstrate the complete method in each workshop. However, we will cover the important steps. We will end with discussion of ideas for different experiments that can be done with the microscope, including measuring the DNA-force extension curve, DNA replication, and DNA cleavage.
1. For an excellent review of the field, see the single molecule theme issue of Annual Reviews of Biochemistry 77 (2008).
2. W. J. Greenleaf, M. T. Woodside, and S. M. Block, "High-resolution single-molecule measurements of biomolecular motion," Annu. Rev. Biophys. Biomol. Struct. 36, 171-190 (2007).
Chaotic fluid mixing and Hamiltonian phase space
Tom Solomon, Bucknell University
Very simple, two-dimensional (2D) fluids flows can exhibit mixing which is chaotic, in the sense that nearby tracers in the flow separate exponentially in time. Furthermore, the equations that describe tracer motion in a 2D flow are equivalent to Hamilton's equations of classical physics; consequently, the real space motion of a tracer in a 2D flow is equivalent to a phase space trajectory of a Hamiltonian system. For these reasons, simple experiments with 2D mixing are ideal for illustrating both the concepts of chaotic dynamics and also for developing an intuition for the value of using a phase space description of dynamical and kinematic processes.
In this workshop, we will discuss junior-level experiments that can be used to explore these topics, using two fluid flows: (a) a "blinking vortex flow" which can be set up in a simple petrie dish with some minimal electronics; and (b) an oscillating vortex chain flow which has become a paradigm in the scientific literature for chaotic mixing. The experiments are imaged from above with a CCD camera and analyzed on a Windows-PC. Individual tracers moving in the flow can be tracked in time; the resulting trajectories can be analyzed to show sensitive dependence on initial conditions and to assemble Poincaré sections that reveal the ordered/chaotic structure of the phase space. The mixing of dye in these systems illustrates the importance of chaotic stretching on larger-scale mixing processes. All of the experimental results can be compared with simple numerical simulations that students can perform. These flow systems are also ideal for independent research projects involving undergraduate students. In fact, in the past 15 years, we have published 17 papers -- 16 with undergrads -- on results from these systems, 4 of which are in Physical Review Letters and one in Nature.
Nanoparticle Scattering of Polarized Light
Ernest Behringer, Eastern Michigan University
Natthi Sharma, Eastern Michigan University
This experiment allows students to explore electric dipole radiation in the optical frequency domain. Here, electric dipoles are induced in polystyrene nanospheres suspended in water by the electric field of a linearly polarized HeNe laser beam and the resulting angular distribution of optical radiation in the plane normal to the incident beam is compared to the expected sin2q distribution.
This experiment is highly flexible, with implementations that span a range of simplicity and cost. Details of the construction of the experiment and analysis of the data will be provided. The polarization, particle size and concentration dependence of the angular distribution, and the radial dependence of the irradiance will be discussed. The apparatus will be available for use and typical results will be presented.
For graduate students, the experiment can be extended easily to the study of magnetic dipole (and/or electric quadrupole) radiation by mounting a polarizer in front of the detector. The experiment serves as a handy teaching tool to elucidate the polarization and angular distribution of low order multipole radiation when teaching multipole fields. Many details are contained in Am. J. Phys. [71,1294 (2003)] and Phys. Rev. Lett. [98, 217402 (2007)].
After doing the experiment, students understand how electric dipole radiation explains polarization by reflection (Brewster’s angle), polarization by scattering, and the polarization of radiation emitted by circulating charges (as in pulsars).
Brownian Motion: Measuring Avogadro's Constant for $70
Beth Parks, Colgate University
Brownian motion played a pivotal role in the development of modern physics. One of the four papers in Einstein's 1905 annus mirabilis explained Brownian Motion using atomic theory. Up until this publication, there were still prominent physicists who believed that atoms were a convenient fiction, but not real objects; Einstein's paper provided the convincing evidence for their existence.
Through measurements of Brownian motion, students can measure a fundamental constant, Avogadro's number, from which they can determine the size of atoms.1 Additionally, they are introduced to a currently active research area-in the past 12 months, there have been 80 manuscripts submitted to cond-mat on Brownian motion.
These inexpensive measurements are made possible by using microscopes from the consumer market, solutions of polystyrene spheres of uniform size, and the image processing software ImageJ available free from the NIH. During this session, participants will learn how to set up the experiments and analyze the data to yield accurate measurements (within a few percent) of Avogadro's number and Boltzmann's constant.
1. "Einstein, Perrin, and the reality of atoms: 1905 revisited," Ronald Newburgh, Joseph Peidle, Wolfgang Rueckner, American Journal of Physics 74 6, June 2006.
Microfluidics Fabrication Workshop
Kevin Seale, Vanderbilt University
Organizers: Kevin Seale and Ron Reiserer from Vanderbilt University Searle Systems Biology and Bioengineering Undergraduate Research Experience (Searle SyBBURE)
This workshop will introduce participants to the fundamentals of UV lithography and PDMS microfabrication of devices. These methods have been developed and used successfully by SyBBURE undergraduates at Vanderbilt to build and implement novel devices for studies of physical, chemical and biological phenomena including nanopumps, valves, mixers, chemical gradient generators and microformulators.
The hands-on portion of the workshop will include:
-- Ratiometric mixing of polydimethylsiloxane polymer epoxy
-- Casting of prefabbed microchannel mixer masters
-- Curing, punching and plasma bonding procedures for device assembly
-- Priming and controlled perfusion of the fabricated device with miscible colored liquids
Hands-on work will be accompanied by a concurrent informational powerpoint presentation with handouts and plenty of opportunity for question and answers. Our objective is to provide a tool kit and resources for professors who may wish to incorporate microfluidic methods into their laboratory courses.
Simple Laser-Induced Fluorescence Setup to Explore Molecular Spectroscopy
Burçin Bayram/Mario Freamat, Miami University
We will demonstrate a relatively simple, affordable and highly visual experiment to explore molecular spectroscopy by measuring the laser-induced fluorescence (LIF) spectrum of the iodine molecules at room temperature. Iodine is a uniquely suited seed molecule for LIF measurements since it conveniently absorbs about 20,000 lines in the 490- to 650-nm visible region of the spectrum and serves excellent example of displaying discrete vibrational bands at moderate resolution and rotational structure at high resolution.
The apparatus consists of a diode laser 532 nm (or a laser pointer), an iodine cell, and a handheld spectrometer. We will scrutinize the LIF spectrum about the potentials associated with the vibrational states of the diatomic molecules and assign spectral lines based on the transition probability between vibrational levels, build vibrational energy level diagram and tabulate Deslandres table, evaluate the harmonic and anharmonic characteristics of two states and thereof the merits of the harmonic approximation for the molecular oscillator, and finally extract the molecular constants such as dissociation energies of the molecular potentials.
In this workshop, the rotational structure is not seen at a resolution of about 0.2 nm, a common limit for commercial ultraviolet-visible spectrometers, but the vibrational features can be easily discerned in the measurement. At the end of the workshop, we will discuss how to determine rotational inertia and rotational temperature if a higher resolution spectrometer is available.
Experimental explorations in instructional laboratories of molecular spectroscopy are instrumental not only in educating students about the quantum mechanical phenomenology ingrained into the microscopic structure of matter, but also familiarize them with the germinal scientific puzzles and revolutionary answers that historically led to the discovery of quantum mechanics. Thus, a great deal of effort was directed in our department toward maintaining an advanced laboratory course focused on spectroscopy of atoms and molecules, for a diverse and solid education of our upper-level physics majors.
Diffusion in Microfluidic Structures
Steve Wonnell, Johns Hopkins University
This is a hands-on workshop in which participants perform one of the eight experiments developed to accompany a junior level biophysics course at the Johns Hopkins University. The year-long course can also be used as an alternative sequence to the sophomore level waves and statistical mechanics courses. The experiments are short and designed to be performed in place of one or at most two discussion sections; this particular experiment has participants using a "lab on a chip" to measure molecular diffusion in water, from which a value for Boltzmann's constant can be found. The concepts of Reynolds number and laminar flow, diffusion, viscous drag, and Einstein's relation underlie this experiment. Video capture with a microscope, analysis of the image data, least-squares fitting, and using microfludic structures to manipulate molecules are some of the techniques utilized. The experiment can be assembled from commercially available apparatus and parts.
Advanced Laboratories in Acoustics and Ultrasonics
Dale Stille/Ron Vogel, University of Iowa
This workshop will consist of three experiments with the following descriptive titles. 1.Acoustic Velocity, Impedance, Reflection, Transmission, Attenuation, and Acoustic Etalons. 2.Experiments in Acoustical Refraction and Diffraction. 3. An introduction to Acousto-Optics. The experiments use acoustical transducers that operate in the frequency range 8 to 18 MHz and are excited by either signal pulses or bursts, depending on the experiment. Acoustical properties of water and a variety of solids are measured, elastic properties of the solids are calculated from these, and several types of devices are analyzed. Single slit and grating diffractors, refractors, thin plates, acoustic etalons, and an acousto-optic modulator are some of the devices. Students doing these labs will become more familiar with the following areas of physics: ultrasonic wave propagation, elastic properties of solids, acoustical and optical etalons, phonon-photon interaction, and acousto-optics.
Doppler-Free Spectroscopy
Dean Hudek, Brown University
In this experiment a tuneable diode laser is used to explore a very narrow wavelength range of rubidium (Rb) near 780 nm. First the students tune the laser to the resonant frequency of Rb. Once resonance has been established a detector is placed in the beam exiting the Rb cell. With a little adjusting the fine structure of rubidium is observed on the scope. Next a technique known as saturation-absorption spectroscopy is employed. The students rearrange the optical setup such that three beams pass through the Rb cell; two in on direction and one in the other. Two opposing beams are adjusted to intersect inside the Rb cell without disturbing the third beam. Detectors collect the light from the two beams going the same direction. The signal from the undisturbed beam is subtracted from the intersected beam. The difference in signals is the hyperfine structure of Rb. Lastly the students set up a Michelson interferometer and use it to calibrate their data. For the full version of our manual go to: https://wiki.brown.edu/confluence/download/attachments/5890/doppler.pdf?version=5&modificationDate=1320259684000
Information on how to acquire the required equipment will be provided at the workshop.
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