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

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Do NOT write on these sheets or take them with you! The next class needs them too! PHYS-1200 PHYSICS II SPRING 2005 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 4.0 meters from the source the intensity of the waves is 0.50 W/m². 1. At what rate is the source radiating energy? That is, what is the power of the source, P s ? P s = 4 π r ² I = 4 (4.0 m)²(0.50 W/m²) = 100 W 2. Find the intensity of the waves at a distance of 10.0 meters from the source. 2 1 r I , so 16 . 0 ) m 10 ( ) m 4 ( ) m 4 ( ) m 10 ( 2 2 = = I I . Then, I (10 m) = 0.16 I (4 m) = 0.16(0.50 W/m²) I (10 m) = 0.08 W/m² 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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This note was uploaded on 09/17/2008 for the course PHYS 1200 taught by Professor Stoler during the Spring '06 term at Rensselaer Polytechnic Institute.

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

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