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Ch33_Lecture_Notes

# Ch33_Lecture_Notes - Chapter 33 Electromagnetic Waves...

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1 Chapter 33 Today’s information age is based almost entirely on the physics of electromagnetic waves. The connection between electric and magnetic fields to produce light is own of the greatest achievements produced by physics, and electromagnetic waves are at the core of many fields in science and engineering. In this chapter we introduce fundamental concepts and explore the properties of electromagnetic waves. Electromagnetic Waves 33-

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2 Fig. 33-1 The wavelength/frequency range in which electromagnetic (EM) waves (light) are visible is only a tiny fraction of the entire electromagnetic spectrum Maxwell’s Rainbow 33- Fig. 33-2
3 An LC oscillator causes currents to flow sinusoidally, which in turn produces oscillating electric and magnetic fields, which then propagate through space as EM waves 33- Fig. 33-3 Oscillation Frequency: 1 LC ϖ = Next slide The Traveling Electromagnetic (EM) Wave, Qualitatively + - I

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4 EM fields at P looking back toward LC oscillator 33- Fig. 33-4 The Traveling Electromagnetic (EM) Wave, Qualitatively 1. Electric and magnetic fields always perpendicular to direction in which wave is travelling transverse wave (Ch. 16) 2. always perpendicular to 3. always gives direction of E B E B E B C C r r r r r r wave travel 4. and vary sinusoidally (in time and space) and are (in step) with each other E B in phase r r + - I + - I
5 33- Fig. 33-5 Mathematical Description of Traveling EM Waves Electric Field: ( 29 sin m E E kx t ϖ = - Magnetic Field: ( 29 sin m B B kx t ϖ = - Wavenumber: 2 k π λ = Angular frequency: 2 π ϖ τ = Vacuum Permittivity: 0 ε Vacuum Permeability: 0 μ Wave Speed: 0 0 1 c μ ε = All EM waves travel at c in vacuum Amplitude Ratio: m m E c B = Magnitude Ratio: ( 29 ( 29 E t c B t = EM Wave Simulation

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6 Unlike all the waves discussed in Chs. 16 and 17, EM waves require no medium through/along which to travel. EM waves can travel through empty space (vacuum)! Speed of light is independent of speed of observer! You could be heading toward a light beam at the speed of light, but you would still measure c as the speed of the beam! A Most Curious Wave 33- 299 792 458 m/s c =
7 Changing magnetic fields produce electric fields, Faraday’s law of induction 33- Fig. 33-6 The Travelling EM Wave, Quantitatively Induced Electric Field ( 29 ( 29 cos and cos m m E B kE kx t B kx t x t ϖ ϖ ϖ = - = - - B d E d s dt Φ = - r r g ( 29 E ds E dE h Eh h dE = + - = r r g ( 29 ( 29 B B h dx Φ = dB dE dB h dE h dx dt dx dt = = - E B x t C = - ( 29 ( 29 cos cos m m m m E kE kx t B kx t c B ϖ ϖ ϖ - = - - = |B| decreasing E induced c x

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8 Changing electric fields produce magnetic fields, Maxwell’s law of induction 33- The Traveling EM Wave, Quantitatively Induced Magnetic Field ( 29 B ds B dB h Bh h dB = - + + = - ur r g ( 29 ( 29 E E d dE E h dx h dx dt dt Φ Φ = = 0 0 dB h dB h dx dt μ ε - = 0 0 B E x t μ ε - = ( 29 ( 29 0 0 cos cos m m kB kx t E kx t ϖ μ ε ϖ ϖ - - = - - Fig. 33-7 ( 29 0 0 0 0 0 0 1 1 1 m m E c c B k c μ ε ϖ μ ε μ ε = = =≡ = B induced
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Ch33_Lecture_Notes - Chapter 33 Electromagnetic Waves...

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