Lecture 10 - EM Waves (24.3)

# Lecture 10 - EM Waves (24.3) - Electro-magnetic waves Ch 24...

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Electro-magnetic waves Ch 24 “One day sir, you may tax it." -- ~1860. Michael Faraday's reply to Gladstone, then British Minister of Finance, when asked about the practical value of electricity.

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What is light? Light is an electro-magnetic wave. Maxwell’s Equations for electric fields (E) and magnetic fields (B) show that a time-varying B field acts to create an E field and vice versa. That is, E and B fields can “sustain each other” and form an “electro-magnetic wave” that propagates through space. Visible light from a light bulb is one example of an electromagnetic wave. TV and radio stations produce electromagnetic waves. The difference between TV and visible light is simply the wavelength.
Frequency : Number of times per second that a crest passes a Fxed point. moves at speed c Longer wavelength => smaller frequency Will see later that higher frequency => higher energy photons

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The electromagnetic spectrum 4000 5000 6000 7000 Wavelength (Angstroms) 1 Angstrom = 10 -10 m
Technically, each color corresponds to light of a speciFc wavelength. When white light passes through a prism, a full optical spectrum results. Violet light is 4000 Red light is 6500

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Electricity and Magnetism: What you have seen before Gauss’s law: the total electric flux through any closed surface equals the net charge inside that surface (divided by ε 0 - the permittivity of free space) e.g. for a charge of value Q sitting at the center of a spherical surface of radius r we have: Coulomb’s Law!
Electricity and Magnetism: What you have seen before Gauss’s law for magnetism: the total Magnetic flux through any closed surface equals zero. (There are no point “magnetic charges”.)

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Electricity and Magnetism: What you have seen before Faraday s Law of induction : “a changing magnetic field creates an electric field”
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## This note was uploaded on 09/08/2008 for the course PHYS 3B taught by Professor Wu during the Spring '08 term at UC Irvine.

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Lecture 10 - EM Waves (24.3) - Electro-magnetic waves Ch 24...

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