Instructors_Guide_Ch25 - 25 Electric Charges and Forces...

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25 Electric Charges and Forces Recommended class days: 3 Background Information Electricity and magnetism occupy a major portion of the introductory physics course—one-third of most texts. Although electricity and magnetism are undeniably important components of science and technology, the level of detail and the level of mathematics reflects more the interests of physi- cists than the needs of students. As noted earlier in this guidebook, the majority of engineering and science disciplines utilize only static electric and magnetic fields. Their interests are much more with understanding basic electric and magnetic phenomena, including the electric and magnetic properties of materials, than with mathematical sophistication. Essentially all current textbooks present electricity and magnetism as a highly abstract, mathematical theory, the most sophisticated mathematics of the introductory physics course. Basic information about electric and magnetic phenomena is introduced quickly, with minimal discussion, as the text moves rapidly into the definitions and properties of fields and potentials. The emphasis is on the formal properties of fields and potentials, and these ideas are only loosely connected with electric and magnetic phenomena. The “mathematization” of electricity and magnetism—the use of vector integrals and the inclusion of Maxwell’s equations—is a fairly recent entry into introductory physics. Unfortunately, only a small minority of students have yet reached vector integrals in their calculus course. For the large majority, this is new and frightening math that obscures the physical concepts of electric and magnetic fields. There is an increasing body of research that we can turn to for guidance. This research has probed student understanding of both basic concepts and theoretical constructs in electricity and magnetism. Unfortunately, much of it is not yet published. Many of the results described in the next few pages are from research reports presented at meetings and from unpublished Ph.D. dissertations. Students have a high level of familiarity with the basic phenomena of mechanics—namely, forces and motion. After all, they’ve spent roughly twenty years moving their own bodies and mov- ing other objects. Although they harbor many misconceptions, they have little difficulty realizing that the Newtonian theory of mechanics is seeking to provide a quantitative explanation of the phenomena of motion. By contrast, a large majority of students have essentially no familiarity with the basic phenomena of electricity and magnetism. For most, their experience is limited to turning on light switches, changing batteries, and using refrigerator magnets—and they hold major misconceptions about all three of these. Surveys of students show that only a small fraction of the men and essen- tially none of the women have ever engaged in hands-on activities with circuits, meters, motors, or magnets. If you hand a student a battery, a flashlight bulb, and a piece of copper wire and ask him
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This note was uploaded on 01/14/2011 for the course CD 254 taught by Professor Kant during the Spring '10 term at Central Oregon Community College.

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Instructors_Guide_Ch25 - 25 Electric Charges and Forces...

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