Material Matters in the Physics Classroom
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Material Matters in the Physics Classroom Chris Chiaverina Science Department, New Trier High School, Winnetka, IL 60093, U.S.A.
ABSTRACT What do fiber optics, superconductors, memory wire, polymers, solid state devices, ferrofluid, rare earth magnets, carbon-based electroacoustic devices, and photonic crystals have in common? They are all products of materials science research. Many of these advances play an important role in improving daily life; all are capable of enhancing the teaching of physics. This paper will address how topics from materials science can be used to ignite student interest by providing the basis for exciting hands-on activities. INTRODUCTION Many topics relating to materials science are found in the physics classroom. These materials can either be the focus of or a supporting element in a physics lesson. This paper contains some of my students’ favorite demonstrations and laboratory activities that use materials ranging from the everyday to the not so common. For the most part, the following student activities and demonstrations represent discrepant events, phenomena that amaze students because they are contrary to what is expected to happen based on the students’ background knowledge. DISCUSSION Electrical activities using various forms of carbon Carbon is the essential to all life on Earth. Carbon is also a very useful material when it comes to extending and amplifying concepts pertaining to electricity and magnetism. What follows are a few of the activities relating to electricity, many of which are quantitative, that can be performed with various forms of carbon. Students are often surprised to learn that charcoal can conduct electricity. They discover this by experimenting with a device known as a binchotan microphone. Binchotan is a type of activated charcoal made from oak, which due to its porous nature, is often used as a water purifier. The binchotan microphone is the creation of a group of amazing Japanese physics teachers called the Stray Cats. They devised a way of showing how changes in resistance can be used to transform sound into an electrical signal with a homemade carbon microphone fashioned from two sticks of binchotan (see figure 1).
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Figure 1. A carbon microphone fashioned from two sticks of binchotan. As is the case with a commercial carbon microphone, sound waves apply varying pressure to the charcoal causing a change in the contact area between the sticks and, with it, a change in resistance. Changes in resistance cause variations in the current in a series circuit that contains batteries and the binchotan, resulting in a recordable electrical signal. A second simple carbon microphone consists of a length of pencil lead resting on two singleedge razor blades. Sound waves cause the pencil lead to move, resulting in changes in res
