3.1 EM Waves

3.1 EM Waves - Electromagnetic waves Electromagnetic Waves...

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1 Electromagnetic Waves 3.1 Maxwell’s equations Electromagnetic waves Speed of light Properties of EM waves James Clerk Maxwell Electromagnetic waves • EM waves carry energy in oscillating electric and magnetic fields that propagate through space with the speed of light. • EM waves are governed by the laws of Electricity and Magnetism applied to a vacuum. • Maxwell showed that these laws (called Maxwell’s equations) give rise to EM waves and correctly predict the speed of light. Electric and Magnetic Fields Capacitor Inductor • Electric and magnetic fields exist in a vacuum. • Electric and magnetic fields store energy E field B field A time varying Magnetic field creates an Electric field Induced Electric field Faraday’s Law B d Ed l dt φ ⋅= J GJ G v Induced Magnetic field i B Ampere’s Law A Magnetic field is produced by a current Maxwell: A magnetic field should be produced by a Changing electric field. Problem with Ampere’s law ii B field What about the B field around the capacitor? Maxwell: a changing E field is equivalent to a current and also produces a B field in a surrounding loop E oo d Bd l dt φ ε µ J G v (in a vacuum) changing E field dE
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2 Maxwell’s Equations in a vacuum o q Eda 0 ⋅==
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3.1 EM Waves - Electromagnetic waves Electromagnetic Waves...

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