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Unformatted text preview: 1 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 one 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- 2 When the amplitude of the oscillator in a series RLC circuit is doubled: A. the impedance is doubled. B. the voltage across the capacitor is halved C. the capacitive reactance is halved D. the power factor is halved E. the current amplitude is doubled 3 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 4 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 Travelling Electromagnetic (EM) Wave, Qualitatively 5 EM fields at P looking back toward LC oscillator 33- Fig. 33-4 The Travelling 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 → × 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 6 33- Fig. 33-5 Mathematical Description of Travelling EM Waves Electric Field: ( 29 sin m E E kx t ϖ =- Magnetic Field: ( 29 sin m B B kx t ϖ =- Wave Speed: 1 c μ ε = Wavenumber: 2 k π λ = Angular frequency: 2 π ϖ τ = Vacuum Permittivity: ε Vacuum Permeability: μ All EM waves travel a c in vacuum Amplitude Ratio: m m E c B = Magnitude Ratio: ( 29 ( 29 E t c B t = EM Wave Simulation 2 7 • 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!...
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This note was uploaded on 12/05/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.
- Spring '08