Christopher G. Deacon

High resolution Raman spectra of near‐critical CO2

The pure vibrational (Q branch) components of both the ν1 and 2ν2 Raman bands of supercritical CO2 have been studied using interferometric techniques. A significant broadening of the ν1 spectrum was observed as the critical point (Tc=304.15 K) was approached along the critical isochore.

Measuring soap bubble thickness with color matching

This paper describes a laboratory experiment designed to measure thickness variations across a soap bubble. The experiment uses the phenomenon of thin film interference and the principles of color perception to measure the thickness of the soap film at various points across the surface of the bubble. The students review the classical theory of interference and use a digital camera to make the measurements. The apparatus required for the experiment is inexpensive and easy to construct. This experiment is suitable for a senior undergraduate course and can potentially be used to study hydrodynamic effects in soap films.

Contact angle of ethanol-water solutions on crystalline and mesoporous silicon

Measurements of contact angle of ethanol?water solutions were performed on crystalline silicon and on mesoporous silicon films with porosities up to ?72%. Water contact angles of 44? and 76? were measured for untreated and HF-dipped crystalline silicon, respectively, consistent with previous studies. The contact angle for ethanol?water mixtures was found to decrease with increasing ethanol concentration for both untreated crystalline silicon and also for HF-dipped crystalline silicon up to an ethanol concentration of ?80%; at higher concentrations the contact angle approached zero. Similar behaviour was observed on mesoporous silicon surfaces for ethanol concentrations ? 40%, above which the contact angle dropped abruptly to an immeasurably small value. This behaviour is attributed to a decrease in surface tension with increasing ethanol concentration. For all ethanol?water solutions, a minimum value of contact angle was observed at a porosity of ?40%, above which it remained approximately constant. The behaviour of contact angle with porosity can be explained by a change in the Wenzel roughness parameter due to changes in the specific surface area of the film.

A simple method of determining Debye temperatures

A simple undergraduate laboratory experiment on the determination of Debye temperatures of solids is described. A sample of the solid is immersed in liquid nitrogen; from the mass of nitrogen boiled off in cooling the solid, the change in its internal energy is determined. The quantum corrections to the classical law of Dulong and Petit are calculated and the Debye temperature is obtained using a simple graphical technique.

The Importance of Graphs in Undergraduate Physics

The graph is a tool for the analysis of data, but like any tool is only as effective as a student’s ability to interpret it in a meaningful way. This article suggests ways that graphs can be plotted to extract the maximum information from an experiment.

Investigating vortex streets behind real and virtual bluff bodies

This paper describes a laboratory experiment designed to study regular arrays of vortices occurring behind an object in a stream of fluid. This phenomenon is observed in industrial flows, flows in the ocean, and in the atmosphere. In the first part of the experiment we consider the flow behind a circular cylinder. In the second part of the experiment the effect of a body on the fluid is imitated by using an appropriate force field, with no real body present in the fluid. The force field (virtual body) is created by a permanent magnet located above the surface of water in combination with an electric current applied in the horizontal direction. The apparatus required for the experiment is inexpensive and easy to construct.

Graduate Teaching Assistants' Perceptions of Teaching Competencies Required for Work in Undergraduate Science Labs.

ABSTRACT Many post-secondary institutions provide training and resources to help GTAs fulfil their teaching roles. However, few programmes focus specifically on the teaching competencies required by GTAs who work with undergraduate students in laboratory settings where learning tends to be more active and inquiry based than in classroom settings. From a review of 8 GTA manuals, we identified 20 competencies and then surveyed faculty and lab coordinators (FIS) and GTAs from a Faculty of Science at a comprehensive Canadian university to identify which of those competencies are required of GTAs who work in undergraduate science labs. GTAs and FIS did not significantly differ in the competencies they view as required for GTAs to work effectively in undergraduate labs. But, when comparing the responses of GTAs and FIS to TA manuals, ‘Clearly and effectively communicates ideas and information with students’ was the only competency for which there was agreement on the level of requirement. We also examined GTAs’ self-efficacy for each of the identified competencies and found no overall relationship between self-efficacy and demographic characteristics, including experience and training. Our results can be used to inform the design of training programmes specifically for GTAs who work in undergraduate science labs, for example, programmes should provide strategies for GTAs to obtain feedback which they can use to enhance their teaching skills. The goal of this study is to improve undergraduate lab instruction in faculties of science and to enhance the teaching experience of GTAs by better preparing them for their role.

A Background to Background Radiation

The study of radiation at the introductory college level usually includes experiments to determine the half-life of a radioactive isotope and also a study of the absorption of nuclear radiation by metal foils. These experiments are straightforward to do using a Geiger-Muller tube and scaler, and allow for the determination of well-known constants. The underlying theory behind these experiments is also easy to understand, but fails to take into account background radiation that will be present, regardless of the source being used. The purpose of this article is to show how students can measure the effect of background radiation on these experiments by modifying the standard textbook theory.

Demonstration experiments with a Stirling engine

Heat engines are used in teaching thermodynamics as ideas to develop theory and real things to illustrate working thermodynamic principles. The Stirling engine combines both possibilities. We use it as a tool to illustrate some basic thermodynamic principles; to show the characteristics of a heat engine and interpret a pV diagram. We also show how the Stirling engine can be used to demonstrate the principles of operation of a refrigerator and heat pump.

A study of drag using a circular air track

A circular air track is used to investigate the drag experienced by a rider as it moves round the track.