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Magnetism
10 questions By Tony R. Kuphaldt
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Question 7 of 10
Define the following terms:
- • Ferromagnetic
- • Paramagnetic
- • Diamagnetic
Reveal answer- • Ferromagnetic: easily magnetized
- • Paramagnetic: only slightly magnetic
- • Diamagnetic: repels magnetic fields
Notes:Ask your students to give examples of a few ferromagnetic materials. This should be quite easy.
An interesting point of trivia to bring up in discussion is that oxygen, even in its gaseous state, is paramagnetic. This principle is exploited in the design of some oxygen concentration analyzer equipment, which measure oxygen content by measuring the amount of force generated by a tiny glass container filled with a solution to be sampled!
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Question 8 of 10
A mechanic visits you one day, carrying a large wrench. She says the wrench became magnetized after setting it near a large magnet. Now the wrench has become an annoyance, attracting all the other tools in her toolbox toward it. Can you think of a way to demagnetize the wrench for her?
Reveal answerAn object may be de-magnetized by careful magnetization in the opposite direction. Incidentally, this is generally not how de-magnetization is done in industry, but it is valid.
Notes:Students may want to test their hypotheses on magnetized paper clips, which are easy to work with and quite inexpensive. It will be interesting to see how many of your students actually researched modern de-magnetization techniques in preparation for answering this question.
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Question 9 of 10
Suppose we needed to shield a sensitive electronic instrument from external magnetic fields. How would you suggest we do such a thing? How can we keep stray magnetic fields away from this instrument?
Reveal answerMagnetic shielding requires that the instrument be completely surrounded by a high-permeability enclosure, such that the enclosure will “conduct” any and all magnetic lines of flux away from the instrument.
Challenge question: should the enclosure material have a high retentivity, or a low retentivity? Explain your answer.
Notes:This question provides a good review of the terms “permeability” and “retentivity”. Discuss these terms as they apply to the subject of magnetic shielding. After discussing these concepts, ask your students to give examples of suitable enclosure materials. What metals would be especially good for shielding purposes? Where did they obtain their information about magnetic shielding?
