F11Physics1CLec24A

# F11Physics1CLec24A - Physics 1C Lecture 24A"There are two...

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Physics 1C Lecture 24A "There are two ways of spreading light: to be the candle or the mirror that reflects it." --Edith Wharton

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Announcements Quiz 1 average 68. Standard deviation 23 ranging from 20s to 100s. EM waves. Polarization. Nature of Light.
Electromagnetic Radiation Power hitting earth from sun is 86,000 TW every year Used for heat, food, transportation World consumes 15 TW every year Problem with fossil fuels is the combustion products are greenhouse gases

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Spherical Waves A spherical wave propagates radially outward from the source (for instance, your cell phone). The energy propagates equally in all directions. The intensity is: The average power is the same through any spherical surface centered on the source. Intensity will decrease as r increases.
Clicker Question 24A-1 The amplitude of the oscillating electric field at your cell phone is 8 μ V/m when you are 10km from the broadcast antenna. What is the electric field amplitude when you are 20km from the antenna? A) 8 μ V/m. B) 4 μ V/m. C) 2 μ V/m. D) 1 μ V/m

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Doppler Effect for Light Since light is an EM wave, if the source or the observer moves with respect to each other the frequency of the wave will be Doppler shifted. But since the speed of light is so large it takes a large relative speed, u , between the observer and the source for there to be any noticeable effect on the observed frequency, f o . For light the Doppler equation becomes: where f s is the frequency emitted by the source and c is the speed of light.
Doppler Effect for Light As with the previous Doppler equation, you take the top sign (positive) if the observer and the source are moving toward each other. You take the

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## This note was uploaded on 12/11/2011 for the course PHYS 1C taught by Professor Smith during the Fall '07 term at UCSD.

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F11Physics1CLec24A - Physics 1C Lecture 24A"There are two...

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