Why no inverse-square law for magnetism?
(Asked by a physics teacher) A student’s question: if magnetism and electricity are unified in theory, then why does the electrical force between two charged particles follow the inverse square law but magnetic attraction or repulsion does not. Any reasonable explanations suitable for high school general physics will be welcome. REPLY Good question, indeed! And it would not have been asked, say, around the year 1800, because at that time, a perfect symmetry DID seem to exist. The experiments of Charles Augustine Coulomb around 1777–see section 5 in http://www.phy6.org/earthmag/mill_4.htm –seemed to indicate that not only Newton’s gravity, but also the force between electric charges and magnetic poles decreased like the inverse square of the distance. Then in 1796 Henry Cavendish, using a similar apparatus (but with much, much greater sensitivity) demonstrated that in the laboratory, too, gravity decreased as the inverse square of distance. But this nice symmetry did not last. Every E
