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chapter34 - Chapter 34 Electromagnetic Waves and light...

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Chapter 34 Electromagnetic Waves and light
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Electromagnetic waves in our life circle6 Microwave oven, EM wave is used to deliver energy. circle6 Radio/TV, cell phones, EM wave is used to carry information. circle6 Telephone and internet: electrical signal in copper wires is NOT EM wave, but fiber optics is the backbone of the network. circle6 The wireless connection for your laptop, the bluetooth headset for your iPod, … Without EM wave, there would be no life on Earth. – why?
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Plane EM waves, the simplest form A review: a wave is a disturbance that propagates through space and time, usually with transference of energy PLAY ACTIVE FIGURE An EM wave is the oscillation between electric and magnetic fields. The electric field oscillates in the x-y plane, along the y direction; the magnetic field oscillates in the x-z plane and along the z direction. The EM wave propagates along the x axis, with the speed of light c , in vacuum. E arrowrightnosp B arrowrightnosp
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Wave propagation A sinusoidal EM wave moves in the x direction with the speed of light c , in vacuum. PLAY ACTIVE FIGURE The electric field direction (here the y axis direction) is called the polarization direction. When this polarization direction does not change with time, it is said that the EM wave is linearly polarized. Another common polarization is the circular polarization, when the electric field direction moves in a circle The magnitudes E and B of the fields depend upon x (the location in the wave) and t (time) only: ( ) max E E cos kx t ω = - ( ) max B B cos kx t ω = - Here k is the wave number.
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Rays, wave front and plane wave circle6 A ray is a line along which the wave travels. circle6 In a homogeneous medium for EM waves (vacuum being one), rays follow straight lines. circle6 The surface that connects points of equal phase in a group of rays (waves) is called the wave front . When this wave front is a geometric plane, this collection of waves is called a plane wave.
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Maxwell’s equations of EM waves
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