22.9 Electromagnetic Waves


In 1687 Sir Isaac Newton published his famous Principia which included his three Laws of Motion that completely described the motion of physical objects. It can be said that all of the study of Mechanics is but finding more ways to apply these Laws of Motion. In 1873 James Clerk Maxwell published A Treatise on Electricity and Magnetism which included his four equations, now known as Maxwell's Equations, that summarized the whole behavior of Electricity and Magnetism as Newton's Laws had for Mechanics.

Maxwell's Equations show a profound and basic connection between Electricity and Magnetism. Electricity and Magnetism are not two separate, distinct items. They are two parts of a unified whole, "Electro-Magnetism". You have already seen how an electric current causes a magnetic field. Maxwell found that a changing magnetic field also causes an electric field. Indeed, you have seen this in your study of Faraday's Law and Induced emf's.

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(c) Doug Davis, 2000; all rights reserved