In many high school teaching materials the force on a current-carrying wire in a magnetic field is discussed using an idea based on a so-called “catapult field” (cf. Fig. 1), an engaging depiction of magnetic forces, albeit one which, to the best of our knowledge, has neither been used in college-level educational material or scrutinized in academic journals. Here we examine carefully the physical basis of the “catapult field” concept, and find both its accuracy and utility seriously questionable.
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To prevent Hall-type effects due to the drift of charges in each conductor, the outer cylinder can be considered to consist of a ring of insulated current-carrying wires, and the radius of the inner wire can be made sufficiently small
(c << a, b
).7.
The appendix can be found at TPT Online, http://dx.doi.org/10.1119/10.0001840, under the Supplemental tab.
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2020
American Association of Physics Teachers
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