June 12, 2005
June 12, 2005
June 15, 2005
10.520.1 - 10.520.11
Electrical Fundamentals - Make Them Come Alive for Students
Walter Banzhaf, P.E.
College of Engineering, Technology, and Architecture University of Hartford, West Hartford, CT 06117
Introduction Many laboratory experiments we ask students to perform in electrical fundamentals laboratory classes are unnecessarily unexciting. Such tasks as determining the current through R7 of a ladder network with eight resistors (does a first-semester student really care about R7, or its current?), or verifying Kirchhoff's Voltage Law in a circuit with only resistors, are all too often devoid of interest to the average student. Nothing in the experiment makes noise, or gives off light, or moves. This paper describes three innovative experiments (constructing a thin-film resistor, constructing a capacitor using a piece of window glass and aluminum foil, and a practical DC constant current source) for a first course in electrical fundamentals which give the student the intended knowledge and practical experience, and, the author feels, have stimulated students' interest in and understanding of the topics they cover.
Construction and Test of a Thin-Film Resistor Resistors are basic circuit elements found in all electronic circuits and come in all manner of formats (cylindrical, SMT, thin- and thick-film), yet students often are exposed only to small cylindrical resistors with values that can range from 0.1 ohm to 22M ohm. The physical parameters that determine resistance are often an unclear and abstract concept, and students have little understanding of the basic formula for a resistor with uniform cross-sectional area: R = ρL/A, where R is the resistance (in Ω), ρ is the resistivity (in Ω-cm), L is the length (in cm), and A is the cross-sectional area (in cm2).
Having each student use the graphite of a pencil to make a "thin film" resistor, and learn by direct and easily understood measurements the effect of length, area and resistivity on resistance, gives a student the kind of understanding of resistance that results from an easy, enjoyable "hands-on" experience. After construction, the student's resistor is used as a rheostat, and then a potentiometer, and as a volume control. Finally each student learns, by experimenting with audio from a CD player, that a tapered resistance works better as a volume control than a linear potentiometer.
How the Resistors are Constructed Students are given a template (see Figure 1 below) and told to use a soft graphite pencil to completely shade in the areas inside the dotted lines, making each area as dark as possible. By doing this they are constructing three thin-film resistors: two are rectangular solids, one is Proceedings of the 2005 American Society for Engineering Education Annual Conference & Exposition Copyright 2005, American Society for Engineering Education
Banzhaf, W. (2005, June), Electrical Fundamentals Make Them Come Alive For Students Paper presented at 2005 Annual Conference, Portland, Oregon. https://peer.asee.org/15384
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