PHY213_Chapter21_Sec8to12-Chapter22_Sec2to4_7

PHY213_Chapter21_Sec8to12-Chapter22_Sec2to4_7 - Chapter 21...

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Chapter 21 / 22 Electromagnetic Waves / Reflection and Refraction
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General Physics Electromagnetic Waves Ch 21, Secs 8–12
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General Physics James Clerk Maxwell 1831 – 1879 Electricity and magnetism were originally thought to be unrelated In 1865, James Clerk Maxwell provided a mathematical theory that showed a close relationship between all electric and magnetic phenomena Electromagnetic theory of light
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General Physics Maxwell’s Starting Points Electric field lines originate on positive charges and terminate on negative charges Magnetic field lines always form closed loops – they do not begin or end anywhere
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General Physics Maxwell’s Starting Points Magnetic fields are generated by moving charges or currents (Ampère’s Law) A varying magnetic field induces an emf and hence an electric field (Faraday’s Law)
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General Physics Turning Faraday’s Law upside down, Maxwell hypothesized that a changing electric field would produce a magnetic field (Maxwell-Ampère’s Law) Maxwell’s Hypothesis
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General Physics Maxwell’s Predictions Maxwell concluded that visible light and all other electromagnetic (EM) waves consist of fluctuating electric and magnetic fields, with each varying field inducing the other Accelerating charges generate these time varying E and B fields Maxwell calculated the speed at which these electromagnetic waves travel in a vacuum – speed of light c = 3.00 x 10 8 m/s
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General Physics Hertz’s Confirmation of Maxwell’s Predictions 1857 – 1894 First to generate and detect electromagnetic waves in a laboratory setting Showed radio waves could be reflected, refracted and diffracted The unit Hz is named for him
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General Physics Hertz’s Experimental Apparatus An induction coil is connected to two large spheres forming a capacitor Oscillations are initiated by short voltage pulses The oscillating current (accelerating charges) generates EM waves
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General Physics Hertz’s Experiment Several meters away from the transmitter is the receiver This consisted of a single loop of wire connected to two spheres When the oscillation frequency of the transmitter and receiver matched, energy transfer occurred between them
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General Physics Hertz’s Conclusions Hertz hypothesized the energy transfer was in the form of waves These are now known to be electromagnetic waves Hertz confirmed Maxwell’s theory by showing the waves existed and had all the properties of light waves (e.g., reflection, refraction, diffraction) They had different frequencies and wavelengths which obeyed the relationship v = f λ for waves v was very close to 3 x 10 8 m/s, the known speed of light
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General Physics EM Waves by an Antenna
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PHY213_Chapter21_Sec8to12-Chapter22_Sec2to4_7 - Chapter 21...

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