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24A light waves

# 24A light waves - Quiz 2 Info Physics 1C Lecture 24A It...

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1 Physics 1C Lecture 24A "There are two ways of spreading light: to be the candle or the mirror that reflects it." --Edith Wharton Quiz 2 Info It will be a Scantron test that covers Chapters 13 and 14. A list of equations, constants, and conversions are available on the website and will be provided on the quiz. You are to write the version of your test on the Scantron form. Get it right to get credit. You will use the Quiz Code Number that you were assigned at the first Quiz. You are expected to abide by UC Policy on Integrity of Scholarship. Electromagnetic Radiation Energy hitting earth from sun is 86,000 TW every year Used for heat, food World consumes 15 TW every year Problem with fossil fuels is the combustion products are greenhouse gases 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 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.

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