Physics 150 Fall 2003
Lect. 10. Electromagnetic Waves and Maxwell
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Summary
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At first sight (and even with many careful experiments)
light appears to have no connection to electricity or magnetism
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Travels at speed c about 300,000,000 m/s (known before Maxwell)
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Light travels in straight lines in vacuum, not affected by magnets or charges
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Maxwell’s (1873) theory of electricity & magnetism
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Four equations that completely determine all of E & M You are NOT responsible for the equations!
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Coulomb's law (already known)
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Ampere's Law - with the generalization made by Maxwell - that a changing
magnetic field causes an electric field
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Faradays Law - a changing
electric field causes an magnetic field
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There are no magnetic charges (the difference between magnetism and electricity)
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( You are NOT responsible for the equations!)
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Predicts that electromagnetic waves travel at a definite speed
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From his equations he predicted the speed would be about 300,000,000 m/s -
the speed of light! Verified to great precision now.
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Light is an electromagnetic wave!
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Other electromagnetic waves (see slides next lecture): radio, X-ray, gamma ray , ....
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What is a wave? (Next lecture) for light what is waving?
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How can light go through free space (vacuum)?
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What does light travel through?
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The "Ether" ?? -- a massless substance invented to carry light??
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Next Time: waves and light as a wave
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Read for Next Time: March, Chapts. 7