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Experimental suitability analysis of iron core materials used in elementary school electromagnet experiment
New Phys.: Sae Mulli
Published online December 14, 2017;  
© 2017 New Physics: Sae Mulli.

Beomgil Choi, Youngseok Jhun*
Received October 30, 2017; Revised December 4, 2017; Accepted December 14, 2017.
Abstract
In elementary school electromagnet experiments, iron nails have been used for a long time as cores, but the large residual magnetic field has been pointed out as a problem. Elementary school teachers know that it is possible to reduce the residual magnetic field by properly heating the iron nail, but since the proper information about the heating conditions and the heating time is not obtained, the nails are heated according to their intuition for their classrooms. In order to eliminate these inconveniences, threaded bolts have been replaced iron nails in electromagnet experiment activity in the textbook for 2009 revision elementary science curriculum because threaded bolts don’t need to be heated as cores of electromagnets. However, we don’t know yet threaded bolts are better as cores than iron nails without sufficient information. In this study, we tried to figure out the magnetic property of iron nails as they are heated in various condition and to compare them with threaded bolts. The nail heated with an alcohol lamp had a problem of remaining residual magnetism after use in the experiment. In order to solve this problem, we have found the conditions to reduce the residual magnetism by changing the intensity of the flame heating, the heating time and the cooling method. In addition, we tried to find suitable material for the electromagnet core by comparing the threaded bolt and the iron nail which have been heated appropriately. As a result of the study, we firstly found out that there is optimized heating time of nails as iron cores for electromagnets and the hot iron nails need to be cooled slowly in the air. Secondly we concluded that properly heat treated iron nails are more useful as electromagnets’ cores than threaded bolts. The difference of residual magnetic fields is not so large while the intensity of induced magnetic filed by electric current in iron nails are 3 times larger than that in threaded bolts.


January 2018, 68 (1)
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