Inverse Square Law Abuse

(The abuse is what happens when people generalize a concept too far.) E = kq/r² shows that electric field varies with distance from a point charge (or spherically symmetric charge distribution) inversely as the square of the distance from the center. This is valid if you have this one charge surrounded by empty space. Fine for fictitious problems illustrating basic principles, but not for real life. In real life, an opposite charge, induced or otherwise, will be nearby, and this will make the field drop off more rapidly than an inverse square. For a dipole, E approaches an inverse cube law variation at a large distance away.

The same thing happens with magnetism. You never have just one pole. The pure magnetic dipole approaches an inverse cube law also.

When the scare about electromagnetic fields came out, meters were sold for doing measurements along with instructions for using the inverse square law in calculations. Totally bogus.

Go back to main E&M etc. page.

Other main physics pages:

mechanics
vibrations and waves
quantum

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