Lecture 20 - Lecture 20 April 1, 2010 Chapter 33...

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1 Lecture 20 April 1, 2010 Chapter 33 Electromagnetic Waves Fundamental concepts and the properties of 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
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Consider: radio waves (r), visible light (v), infrared light (i), x-rays (x), and ultraviolet light (u). In order of increasing frequency, they are: 1 2 3 4 5 20% 20% 20% 20% 20% 1. r, v, i, x, u 2. r, i, v, u, x 3. i, r, v, u, x 4. i, v, r, u, x 5. r, i, v, x, u
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4 33.3 A certain laser emits light in a narrow band of wavelengths centered at 620.8 nm and with a ''wavelength width'' (such as on the scale of figure 33-1) of 0.0111 nm. What is the corresponding ''frequency width'' in hertz for the emission?
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5 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  Next slide The Travelling Electromagnetic (EM) Wave, Qualitatively
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6 33.5 What inductance must be connected to a 15 pF capacitor in an oscillator capable of generating 430 nm (i.e., visible) electromagnetic waves?
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7 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 EB wave travel 4. and vary sinusoidally (in time and space) and are (in step) with each other in phase
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8 33- Fig. 33-5 Mathematical Description of Travelling EM Waves Electric Field:   sin m E E kx t  Magnetic Field:   m B B t Wave Speed: 00 1 c  Wavenumber: 2 k Angular frequency: 2 Vacuum Permittivity: 0 Vacuum Permeability: 0 All EM waves travel a c in vacuum Amplitude Ratio: m m E c B Magnitude Ratio:     Et c Bt EM Wave Simulation
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9 33.16 An electromagnetic wave with frequency 4.05 × 10 14 Hz travels through vacuum in the positive direction of an x axis. The wave has its electric field directed parallel to the y axis, with amplitude E m . At time t = 0, the electric field at point P on the x axis has a value of + E m /4 and is decreasing with time. What is the distance (in nm) along the x axis from point P to the first point with E = 0 if we search in (a) the negative direction and (b) the positive direction of the x axis? Assume that the speed of light is 2.998*10 8 m/s.
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10 • 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)!
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This note was uploaded on 09/06/2010 for the course PHYSIC 021 taught by Professor Ying during the Spring '10 term at Lehigh University .

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Lecture 20 - Lecture 20 April 1, 2010 Chapter 33...

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