p2f10_lec10_intensity_refraction_and_interference

p2f10_lec10_intensity_refraction_and_interference - Physics...

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Unformatted text preview: Physics 1200 Class 10 Wave intensity Poynting vector Sound level Test Q&A (after) Interference Refraction Two-slit Interference Intensity: a definition Intensity is defined as the average rate of energy transfer (power, P ) per area, through a surface. The units of intensity are watts/meter (W/m 2 ). A P I = Intensity and EM waves tells us the intensity and direction of an EM wave. varies with time. We work with the time- averaged Poynting vector, ( Intensity) . 1 Poynting vector S E B = = r r r 1 1 2 m m I S EB E B = = = S r S r Because E m = cB m , the expression for intensity can be written: 2 2 2 2 m m E cB I c = = Sound wave intensity 2 2 1 2 where is displacement amp. m m I v s s = 2 2 where is pressure amp. m m p I p v = Sound level, , is defined as: 10log I I = where I = 10-12 W/m (the lower limit of human hearing) Interference Waves of the same frequency from two sources will add together at each point in space (superposition principle). If the phases of the two waves are different, interference effects occur. (remember phasors?) = 2 For two equal waves of intensity I and phase difference 4 cos 2 total I I Origins of phase difference...
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This note was uploaded on 10/17/2011 for the course PHYS 1010 taught by Professor Schroeder during the Spring '07 term at Rensselaer Polytechnic Institute.

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p2f10_lec10_intensity_refraction_and_interference - Physics...

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