act18ans - Do NOT write on these sheets or take them with...

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Unformatted text preview: Do NOT write on these sheets or take them with you! The next class needs them too! PHYS-1200 PHYSICS II SPRING 2006 Class 18 Activity: Intensity of Waves SOLUTION A . Suppose that waves are being emitted uniformly in all directions from a source, and the waves do not lose energy as they propagate. At a distance of 5.0 meters from the source the intensity of the waves is 0.50 W/m. 1. At what rate is the source radiating energy? That is, what is the power of the source, P s ? P s = 4 r I = 4 (5.0 m)(0.50 W/m) = 157 W 2. Find the intensity of the waves at a distance of 10.0 meters from the source. 2 1 r I , so 25 . ) m 10 ( ) m 5 ( ) m 5 ( ) m 10 ( 2 2 = = I I . Then, I (10 m) = 0.25 I (5 m) = 0.25(0.50 W/m) I (10 m) = 0.125 W/m B . Now suppose that the radiation from the source that was used in part A is confined to a small angle, so that it does not spread uniformly over the surface of a sphere. Instead, all of the radiation passes through a spot that is 1/100 times the area of the sphere....
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act18ans - Do NOT write on these sheets or take them with...

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