Physical Laboratory Experiment Research Articles

Flow under standing waves: Part 1. Shear stress distribution, energy flux and steady streaming

The conditions for energy flux, momentum flux and the resulting streaming velocity are analysed for standing waves formed in front of a fully reflecting wall. The exchange of energy between the outer wave motion and the near bed oscillatory boundary layer is considered, determining the horizontal energy flux inside and outside the boundary layer. The momentum balance, the mean shear stress and the resulting time averaged streaming velocities are determined. For a laminar bed boundary layer the analysis of the wave drift gives results similar to the original work of Longuet–Higgins from 1953. The work is extended to turbulent bed boundary layers by application of a numerical model. The similarities and differences between laminar and turbulent flow conditions are discussed, and quantitative results for the magnitude of the mean shear stress and drift velocity are presented. Full two-dimensional simulations of standing waves have also been made by application of a general purpose Navier–Stokes solver. The results agree well with those obtained by the boundary layer analysis. Wave reflection from a plane sloping wall is also investigated by using the same numerical model and by physical laboratory experiments. The phase shift of the reflected wave train is compared with theoretical and empirical models.

Transition rate of the Unruh–DeWitt detector in curved spacetime

We examine the Unruh–DeWitt particle detector coupled to a scalar field in an arbitrary Hadamard state in four-dimensional curved spacetime. Using smooth switching functions to turn on and off the interaction, we obtain a regulator-free integral formula for the total excitation probability, and we show that an instantaneous transition rate can be recovered in a suitable limit. Previous results in Minkowski space are recovered as a special case. As applications, we consider an inertial detector in the Rindler vacuum and a detector at rest in a static Newtonian gravitational field. Gravitational corrections to decay rates in atomic physics laboratory experiments on the surface of the Earth are estimated to be suppressed by 42 orders of magnitude.

ATR–FTIR Spectroscopy in the Undergraduate Chemistry Laboratory. Part II: A Physical Chemistry Laboratory Experiment on Surface Adsorption

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy is a useful technique for measuring the infrared spectra of solids and liquids as well as probing adsorption on particle surfaces. The use of FTIR-ATR spectroscopy in organic and inorganic chemistry laboratory courses as well as in undergraduate research was presented in Part I as well as background information and the fundamentals of the ATR-FTIR technique. In Part II, the use of ATR-FTIR spectroscopy in the upper-level physical chemistry laboratories is discussed. A new experiment involving the adsorption of ions from solution onto oxide particle surfaces is introduced. In this laboratory experiment, students use ATR-FTIR spectroscopy to determine the Langmuir adsorption constant, Kads, for sulfate ion adsorbed on 2 particles at pH = 3. A thin film of oxide particles deposited onto the ZnSe ATR element is exposed to solutions of different sulfate concentrations. The infrared spectrum of adsorbed sulfate can be measured in this way. This experiment, which can be easily implemented into an upper-level chemistry curriculum, introduces students to several concepts including surface adsorption, oxide surface chemistry, and environmental interfacial processes.

Doctor Julius Robert Mayer and Energy Processes in Living Systems

The overwhelming majority of important papers in physics are written by physicists. But the physician Julius Robert Mayer (1814–1878, see photo) did a valid theoretical calculation of the mechanical equivalent of heat just before Joule reported on his results from his well-known paddle-wheel experiments. Joule is well-known to physics people and Mayer is a relatively obscure and unknown name. Joule was part of the physics establishment; Mayer was not. Joule's paddle-wheel experiments were easy to understand, and physics people appreciated the painstaking manner in which he made corrections in his experiments. The fame of Joule is well-deserved. On the other hand, Mayer's work is not traditional and there will almost certainly never be a Mayer physics laboratory experiment. We can admire the tenacity with which Mayer pushed his priority case, but that is all.

Raman scattering spectroscopy of liquid nitrogen molecules: An advanced undergraduate physics laboratory experiment

We describe a straightforward and highly visual experiment designed to demonstrate Raman scattering spectroscopy by measuring the vibrational energy spacing of nitrogen molecules in the liquid phase. Interpretation of the spectrum teaches the principles of elastic and inelastic light scattering and the intrinsic properties of molecules. The use of a pulsed Nd:YAG laser with high peak power leads to a plethora of nonlinear optical phenomena. The presence of highly visible stimulated Raman scattering greatly enhances the normal Raman-shifted signal, allowing for a more engaging laboratory experience in comparison to traditional Raman scattering experiments.

High-Resolution Vibration–Rotation Spectroscopy of CO2: Understanding the Boltzmann Distribution

In this undergraduate physical chemistry laboratory experiment, students acquire a high-resolution infrared absorption spectrum of carbon dioxide and use their data to show that the rotational�vibrational state populations follow a Boltzmann distribution. Data are acquired with a mid-infrared laser source and infrared detector. Appropriate absorption peak assignments are made by comparison of the experimental spectrum with the high-resolution transmission molecular absorption (HITRAN) database. Integrated absorption peak areas are used as a measure of relative rotational�vibrational state populations. The effect of temperature on the population distribution is explored by sampling the absorption spectrum at several different temperatures, giving students the opportunity to observe the properties of a Boltzmann distribution.

Ion acoustic wave experiments in a high school plasma physics laboratory

We describe a successful alliance between a university and several high schools. The alliance is centered on a laboratory experiment constructed by students and faculty. The experiment involves sophisticated concepts and equipment not readily available in high schools. Much of the experiment is directly related to the science and mathematics learned in high school, with opportunities to extend their understanding by applying it to a research experience. The experiment is in plasma physics, but a similar alliance can be implemented in any area of science. Although the number of high school students affected by any one alliance is small, the impact is potentially large in the scientific life of a participating student or teacher.

Viscosity by Fluorescence Depolarization of Probe Molecules. A Physical Chemistry Laboratory Experiment

This two-session undergraduate laboratory experiment in physical chemistry involves the measurement of the viscosity of solutions using both a conventional method and a new method based on the fluorescence depolarization of a probe molecule. By comparing the results of the two approaches, students will come to a fundamental understanding of how a macroscopic property (viscosity) and molecular-level properties (molecular dynamics parameters) relate. They will also further their understanding of the physical chemistry of fluorescence and learn how to perform spectroscopic measurements where polarization conditions are important. The experiment also has ramifications in the practical world, because the optical approach has shown promise as the basis for a sensor for in situ viscosity measurement.

Experimental Control of Simple Pendulum Model

This paper conveys information about a Physics laboratory experiment for students with some theoretical knowledge about oscillatory motion. Students construct a simple pendulum that behaves as an ideal one, and analyze model assumption incidence on its period. The following aspects are quantitatively analyzed: vanishing friction, small amplitude, not extensible string, point mass of the body, and vanishing mass of the string.

More things than are dreamt of in your biology: Information-processing in biologically inspired robots

Animals and robots perceiving and acting in a world require an ontology that accommodates entities, processes, states of affairs, etc., in their environment. If the perceived environment includes information-processing systems, the ontology should reflect that. Scientists studying such systems need an ontology that includes the first-order ontology characterising physical phenomena, the second-order ontology characterising perceivers of physical phenomena, and a (recursive) third order ontology characterising perceivers of perceivers, including introspectors. We argue that second- and third-order ontologies refer to contents of virtual machines and examine requirements for scientific investigation of combined virtual and physical machines, such as animals and robots. We show how the CogAff architecture schema, combining reactive, deliberative, and meta-management categories, provides a first draft schematic third-order ontology for describing a wide range of natural and artificial agents. Many previously proposed architectures use only a subset of CogAff, including subsumption architectures, contention-scheduling systems, architectures with ‘executive functions’ and a variety of types of ‘Omega’ architectures. Adding a multiply-connected, fast-acting ‘alarm’ mechanism within the CogAff framework accounts for several varieties of emotions. H-CogAff, a special case of CogAff, is postulated as a minimal architecture specification for a human-like system. We illustrate use of the CogAff schema in comparing H-CogAff with Clarion, a well known architecture. One implication is that reliance on concepts tied to observation and experiment can harmfully restrict explanatory theorising, since what an information processor is doing cannot, in general, be determined by using the standard observational techniques of the physical sciences or laboratory experiments. Like theoretical physics, cognitive science needs to be highly speculative to make progress.

Thin-Lens Equation Nomograph

A simple nomograph based on a general result from analytical geometry can be used to represent the solution of any problem in which the sum of reciprocals equals another reciprocal — that is, the equation that generates the hyperbolic function. One such relationship is the thin-lens formula often used in introductory physics courses. This discussion will show that the nomograph is necessarily consistent with both the ray diagram for a thin lens and the object-image distance relationship obtained in the typical introductory physics laboratory experiment to determine the focal length of a thin lens. It is also useful to display the focal length of the thin lens on the graph obtained in such an experiment.

Melt redistribution during the bending of a porous, partially melted layer

A numerical, poro‐viscoelastic finite element flow model has been developed to simulate the redistribution of melt during the folding of a horizontal layer. Important mechanical properties governing the overall rheology of the buckling layer, including porosity, matrix viscosity, melt pressure and changes in deviatoric stress are tracked simultaneously with deformation. Melt migrates down gradients in melt pressure to the outer hinge zone of the folds, away from sites of compression to regions of local tension. For a matrix with dynamic power law rheology, deformation results in the formation of low viscosity, strain weakening zones that coincide with zones of enhanced deviatoric stress that are potential sites for plastic deformation. During fast deformation of layers with large width to height ratios, the more rapidly bending material splits into domains of higher viscosity separated by lower viscosity zones. Porosity (melt fraction) distribution patterns do not appear to be controlled by the matrix rheology. The numerical results and predictions of melt distribution and geometry during deformation correspond well with data from some physical (analogue) laboratory experiments and field observations. The quantitative nature of our results should help refine more qualitative models for the rates and mechanisms of melt extraction and transport in folded crustal migmatite terranes.

Cost-Effective Spectroscopic Instrumentation for the Physical Chemistry Laboratory

Teaching or developing experiments for an undergraduate physical chemistry laboratory course can be very challenging. Often it is difficult to develop particular experiments because the spectroscopic instrumentation is not readily available within your department or is too expensive to purchase for an undergraduate laboratory experiment. To address these issues, we purchased a series of modular miniature UV–vis fiber-optic spectrometers from Ocean Optics Inc. to conduct undergraduate physical chemistry laboratory experiments. The instrumentation is very modular and can be used for a variety of absorption, emission, or Raman scattering experiments. Instrumentation can also be used in a standard undergraduate instrumental analysis course. The physical chemistry laboratory experiments that we developed with this new instrumentation consist of analyzing the Balmer emission lines of the hydrogen atom, studying nitrogen emission band lines, investigating the absorption spectrum of iodine, and analyzing the Rama...

Control Experimental del Modelo de Péndulo Matemático

Se aportan consideraciones sobre un trabajo práctico de laboratorio de Física destinado a alumnos con conocimientos teóricos sobre oscilaciones. Se propone a los estudiantes construir un péndulo que se comporte como matemático, y realizar un análisis del error introducido por los supuestos del modelo. Entre ellos, se analizan cuantitativamente: rozamiento despreciable, amplitud pequeña, hilo inextensible, masa puntual del cuerpo, masa despreciable del hilo. Se concluye que los supuestos del modelo se pueden cumplir fácilmente en un caso práctico, y que su análisis permite que los estudiantes adquieran una mejor comprensión del modo científico de controlar la validez de los desarrollos teóricos y valoren la importancia y la utilidad de los modelos sencillos en la ciencia.

Quantifying Meniscus Forces with an Electronic Balance: Direct Measurement of Liquid Surface Tension. A Physical Chemistry Experiment

The phenomenon of capillary adhesion, in which a drop of liquid placed between two solid surfaces attracts them together, is considered at an elementary level. It is shown that for a small amount of liquid, independent of the solids-contact geometry, the adhesion force is defined mainly by the Laplace pressure force FL, for which a generalized equation is derived under arbitrary contact geometry. A simple physical chemistry laboratory experiment for measuring FL between a glass sphere and a glass plate with an ordinary electronic balance is described. The relationship between FL and liquid surface tension γ is used to obtain γ. The validity and acceptability of this method for undergraduate physical chemistry laboratories is experimentally confirmed for various liquid samples.

Rare Gas Viscosities: A Learning Tool

The viscosities, η, of the rare gases and SF6 are determined in a physical chemistry laboratory experiment using the evacuation method, which is based on Poiseuille's equation. Students become aware that η does not vary monotonically with row number (or atomic mass) and confirm this behavior on the basis of the kinetic theory expression for η. They find that the collision diameters of the gases, σ, which are obtained from η values, increase monotonically with molar mass, as expected. Students can show that values of σ obtained from gas viscosities agree reasonably well with ab initio calculations of atomic (molecular) diameters using Gaussian 98W.

What Do We Expect From Students' Physics Laboratory Experiments?

We want physics specialized high school and college students to think like physicists, and this involves an understanding of the scientific methods of inquiry and the ability to use these methods in their own investigations. In order to do that, students have to be made aware that no experimental result has any physical meaning unless an estimate of the uncertainty or precision is assigned to it. In this paper, we describe two simple experiments in which high school and college students measure physical constants, and make an easy analysis of their experimental data by applying the tools offered by microcomputers.

Teaching the Fundamentals of Pulsed NMR Spectroscopy in an Undergraduate Physical Chemistry Laboratory

Pulsed nuclear magnetic resonance (NMR) spectroscopy has become the premiere technique for chemists and biochemists studying the conformational, structural, and dynamic properties of a wide variety of molecular and biological systems. The theories and physical concepts associated with pulsed NMR spectroscopy are difficult for undergraduate students to comprehend and often require a thorough understanding of spin physics. Additionally, undergraduates in a laboratory course often consider a pulsed NMR spectrometer to be a "black box" and do not really understand how it operates. To address these issues, we developed an undergraduate physical chemistry laboratory experiment that utilizes a commercially available bench-top pulsed NMR spectrometer. In this experiment, the students assemble the components of an NMR spectrometer, program a variety of pulse sequences, and collect T1 and T2 relaxation data.

Surface Oxidation Kinetics: A Scanning Tunneling Microscopy Experiment

The study of surfaces and materials is underrepresented in the undergraduate chemistry curriculum. This is unfortunate because chemistry plays such a central role in the development of new materials. We have developed an undergraduate physical chemistry laboratory experiment in which students use the scanning tunneling microscope to study the oxidation of graphite by nitric oxide. The lab is designed to simulate a research experience. Each student is responsible for one part of the experiment and the whole class uses everyone's data for their analysis. A scanning tunneling microscope is used to measure the diameter of monolayer pits etched into the graphite by the nitric oxide. The results are both instructive and aesthetic. The data are used to determine the activation energy for the etching process. Several concepts that are explored from these results: crystallography, surface diffusion, bonding, defects, and reaction kinetics. We believe that the open-ended nature of both this experiment and the data analysis will result in better educated and more productive scientists.

Calibrating Frequency Data Collection Systems Using Shortwave Radio Signals

The atomic-clock-derived audio tones broadcast on the National Institute of Standards and Technology (NIST) shortwave station WWV are used to calibrate computer frequency data collection systems via Fast Fourier Transforms (FFT). Once calibrated, the data collection system can be used to accurately determine the audio signals used in several instructional physical chemistry laboratory experiments. This method can be applied to virtually any hardware-software configuration that allows adjustment of the apparent time scale (digitizing rate) of the recorded audio file.