Chapter 33a - Chapter 33 Electromagnetic Waves...

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Chapter 33: Electromagnetic Waves Electromagnetic waves around us. The spectrum of electromagnetic waves - Maxwell’s rainbow. The traveling electromagnetic wave. Induced magnetic field. Induced electric field. Energy transport, Poynting vector. Ch. 33: Electromagnetic Waves - Part A 1 November 9, 2009
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Electromagnetic Waves Global communications and the information technology is based on the transmission of l t ti electromagnetic waves. Radio, telephone - landline and mobile, television internet television, internet, ... Medical applications - X-rays, MRI, ... Ch. 33: Electromagnetic Waves - Part A 2 November 9, 2009
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Electromagnetic Waves The dominant source of EM radiation on Earth is the Sun. Other natural sources of EM - cosmic radiation (intra- and inter-galactic), radioactive materials lightning radioactive materials, lightning, ... Ch. 33: Electromagnetic Waves - Part A 3 November 9, 2009
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Electromagnetic Waves James Clerk Maxwell showed that a beam of light is a traveling wave of electric and ti fi ld l t ti magnetic fields, or an electromagnetic wave. The study of visible light or optics is a part The study of visible light or optics is a part of electromagnetism. Ch. 33: Electromagnetic Waves - Part A 4 November 9, 2009
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The Spectrum of EM Waves Maxwell’s rainbow. Ch. 33: Electromagnetic Waves - Part A 5 November 9, 2009
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The Spectrum of EM Waves Sensitivity of the human eye. 430 - 690 nm 430 690 nm visible light Sensitivity of the human ear. 20 - 22,000 Hz Ch. 33: Electromagnetic Waves - Part A 6 November 9, 2009 20 22,000 Hz
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The Traveling Electromagnetic Wave Generation of EM waves ( ~ 1m, short-wave radio). An LC oscillator produces an AC or oscillatory current at an angular frequency of . An external energy source supplies energy to t f th th l l d th 1/ LC compensate for the thermal loss and the energy carried away by the radiated EM wave. The LC oscillator is coupled by a transformer and Ch. 33: Electromagnetic Waves - Part A 7 November 9, 2009 The LC oscillator is coupled by a transformer and a transmission line to an antenna.
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The Traveling Electromagnetic Wave The antenna consists of two thin solid conducting rods. The current (and charge) oscillates along the rods with the same angular frequency as the LC rods with the same angular frequency as the LC oscillator. The antenna has the effect of an electric dipole whose electric dipole moment (and electric field ) varies sinusoidally in magnitude and direction along the antenna Since the current varies the magnetic field Ch. 33: Electromagnetic Waves - Part A 8 November 9, 2009 antenna. Since the current varies, the produced by the current varies sinusoidally as well.
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The Traveling Electromagnetic Wave The changes in the E and B fields do not happen everywhere simultaneously, but travel outward from
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