Contents of YapMacIsaacMotors2.docGo to page 1 of 8Go to page 2 of 8Go to page 3 of 8Go to page 4 of 8Go to page 5 of 8Go to page 6 of 8Go to page 7 of 8Go to page 8 of 8Contents of Figure 1 (Figure 1.JPG)Contents of Figure 2 (Figure 2.JPG)Contents of Figure 3 (Figure 3.JPG)Contents of Figure 4 (Figure 4.JPG)3/31/2006 1/8 Analyzing Simple Electric Motors in the ClassroomJeff Yap, Dept. of Physics, SUNY-Buffalo State College, 1300 Elmwood Ave, Buffalo,NY 14222 < [email protected]>Dan MacIsaac, Dept. of Physics, SUNY-Buffalo State College, 1300 Elmwood Ave,SC222, Buffalo, NY 14222 <[email protected]>Keywords: electromagnetic, motor, modelingPACS codes: 01.50M, 41.01A, 85.90Abstract:Electromagnetic phenomena and devices such as motors are typically unfamiliarto both teachers and students. To better visualize and illustrate the abstractconcepts (such as magnetic fields) underlying electricity and magnetism, wesuggest that students construct and analyze the operation of a simply-constructedJohnson electric motor. In this paper, we describe a classroom activity that elicitsstudent analysis to aid the comprehension and retention of electromagneticinteractions. (REF1)Acknowledgements:This manuscript partially addressed requirements for the PHY690: Masters’ Project atSUNY-Buffalo State College.We describe the construction, conceptual and introductory level mathematicalanalysis of a simple handmade electric motor. Constructing and analyzing a simplemotor provides students with a fun and interesting hands-on experience that helps makeconcrete complex abstract ideas like the magnetic field due to loops and coils, magneticfield due to a permanent magnet, flux, torque, back EMF, and so forth (Ref 1-5).The motivation for teaching electricity and magnetism using experiential and hands-on activities is that by seeing and feeling the effects, students contextualize theinformation in reality and everyday experience (REF2; REF3). Magnetic field lines,electron flow, and cross products are abstract concepts and models that are often easier topresent for memorization than to internalize in context. If students are kinestheticallysupported in their learning by directly observing and touching concrete applications ofconcepts, the abstract and arcane becomes reality. Building and observing a simplemotor will foster conceptual development and help students assimilate electromagnetism.(REF4) Students typically consider electric motors to be black boxes. Even individualswho have disassembled simple motors can have difficulty understanding the relationshipbetween the wire coils, the magnets, and the electricity (REF5). Construction andoperation of their own personal motor will not only empower the students, it will confirmthe reliability of the physical principles. If students with no previous motor expertise areConfidential: not for distribution. Submitted to Institute of Physics Publishing for peer review on 31 March 20063/31/2006 2/8 able to construct functioning motors, then the concepts cannot possibly be too complex tounderstand. Instructional goals for this activity include the right hand rule and interactionof magnetic fields in devices.Materials for this activity are available from various vendors. The ceramic magnetsshown are part number CB60 from Master Magnetics (http://www.magnetsource.com).Motor wire is widely available, and should be approximately 14-16 gauge, enamelcoated, solid copper wire. Inexpensive wire may also be available (in shorter lengths)from a local motor winding factory. Standard D-Cell batteries and large paperclips arealso necessary for this activity. D-Cell batteries are capable of supplying 5-8 amps ofcurrent during a short circuit, so please be careful.To construct a Johnson (REF6) motor, wrap insulated wire around a D cell batteryforming a coil, extend the two wire ends outward from the loop for armatures, andselectively remove the insulation from the armatures. Current runs through the coil frompaperclips connecting the two poles of the D cell battery to the armatures, and a magnetstuck to the side of the battery supplies a fixed magnetic field. To expedite the activity,these coils can be pre-wrapped and prepared by a teacher or student assistant. There is acertain level of difficulty in winding multiple armatures. Perfect symmetry and weightbalance are not essential, but the armature needs to be fairly balanced to function.While it is rewarding to see misshapen armatures spin, it requires a certain amount ofpractice and repetition to be able to create very reliable armatures. However, if studentshave sufficient time and guidance for building their own armatures, they are able toobserve the construction process from start to finish, and may find complete constructionmore educational. Another solution to save time is to pre-fabricate all of the armatures,but manufacture one in front of the class.The students should be told to leave an interrupter (an area of intact insulation on oneor both of the armatures) which will reduce the tendency of the armature to lock up in aspecific position (REF7). This concept can be addressed later in the class discussion.Once basic armatures are fabricated and observed, variations include increasing ordecreasing the number of loops in the coil, creating a bigger or smaller loop, and alteringthe shape of the coil. The benefit of these changes are to allow the students to makeempirical observations, compare the behaviors with the standard motor, and begin tofigure out how the different variables relate to each other. This is a precursor step toderiving equations based on their knowledge and experience. After initial observationsand experiments have been made, a permanent fixture can be constructed or given toallow hands-free observations and manipulation.As a prerequisite activity to the Johnson motor, students should be made familiar withmagnetic field lines by having used compasses to map and sketch magnetic fields frompermanent magnets. In a similar fashion, students should have mapped magnetic fieldscreated by a current carrying wire to connect electrical current to magnetism. Usingsuspended iron fillings, a ferro-fluid, or several compasses, students will map the areasurrounding a wire. A third pre-requisite hands-on activity is kinesthetically feeling theforces and resulting torques induced when two magnets are brought close together in3/31/2006 3/8 various alignments. Following this activity, students should be given the
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