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Q & A: magnetic baloney for kids

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Most recent answer: 06/16/2015
Q:
http://www.brightideaspress.com/wp-content/uploads/SampleFiles/CKEP_Sample.pdf
This is from a text intended to introduce magnetism to kids.
- Mike W. (age 65)
Urbana, IL
A:

This is a free online excerpt from a physics book for kids. If the part of the book that the authors choose to display is full of errors, one wonders how bad the rest is.

They write: "There are only three types of matter that become magnets", by which they mean iron, nickel an cobalt. Of course, there are zillions of types of matter that become magnets, including the neodymium alloys used in many modern devices. What they must have meant was that there are three pure elements that are ferromagnets at room temperature. They also write that "A permanent magnet is made of some kind of metal", but there are plenty of insulating (non-metallic) magnetic materials. The familiar hematite is one example and several types of garnets are others. They also say that all magnets have north and south poles, but toroidal magnets don't. Oddly, they describe the idea that the Earth's magnetic field comes from electrical currents as "one theory",  as if there were some controversy about it.

But those errors probably wouldn't merit our coveted "Baloney" status. Much more serious, they write that a material becomes magnetic when "a majority of the electrons in the magnet move in one direction". That's baloney- the electrons in a permanent magnet are not all rushing off to one end of the magnet and beyond. After some discussion along these lines, they suddenly switch to a (correct) description of lining up electron spins. Then they go back to the incorrect description in their review questions. 

In some ways it's worse to be so inconsistent than to be just wrong. The authors must be assuming that the kids aren't really paying attention, otherwise they would notice that the book don't have its story straight. 

(BTW, yes the Earth's field comes from current loops, not unidirectional currents, and no the fields of ordinary magnetic materials are almost entirely from spin. So we do have our own story straight.)

Mike W.


(published on 06/16/2015)

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