chapter34

chapter34 - Chapter 34 Electromagnetic Waves and light...

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Unformatted text preview: Chapter 34 Electromagnetic Waves and light Electromagnetic waves in our life Microwave oven, EM wave is used to deliver energy. Radio/TV, cell phones, EM wave is used to carry information. Telephone and internet: electrical signal in copper wires is NOT EM wave, but fiber optics is the backbone of the network. The wireless connection for your laptop, the bluetooth headset for your iPod, Without EM wave, there would be no life on Earth. why? 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 r B r 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: ( 29 max E E cos kx t =- ( 29 max B B cos kx t =- Here k is the wave number. Rays, wave front and plane wave A ray is a line along which the wave travels....
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chapter34 - Chapter 34 Electromagnetic Waves and light...

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