Catapult Description of Magnetic Fields and Forces

摘要

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.