23_Ch 21 College Physics ProblemCH21 Alternating Current Circuits and Electromagnetic Waves

23_Ch 21 College Physics ProblemCH21 Alternating Current Circuits and Electromagnetic Waves

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Alternating Current Circuits and Electromagnetic Waves 223 (b) The intensity of an electromagnetic wave is proportional to the square of its amplitude. If 67% of the incident intensity of the red light is absorbed, then the intensity of the emerging wave is ( ) 100% 67% 33% = of the incident intensity, or 0.33 f i I = I . Hence, we must have max, max, 0.33 f f i i E I E I = = 0.57 = 21.46 If I is the incident intensity of a light beam, and I is the intensity of the beam after passing through length L of a fluid having concentration C of absorbing molecules, the Beer-Lambert law states that 0 ( ) 10 0 log I I CL ε = − where ε is a constant. For 660-nm light, the absorbing molecules are oxygenated hemoglobin. Thus, if 33% of this wavelength light is transmitted through blood, the concentration of oxygenated hemoglobin in the blood is ( ) 10 2 log 0.33 HBO C L ε = ( [1] The absorbing molecules for 940-nm light are deoxygenated hemoglobin, so if 76% of
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