Oxygenated hemoglobin absorbs weakly in the red (hence its red color) and strong
ID: 2308876 • Letter: O
Question
Oxygenated hemoglobin absorbs weakly in the red (hence its red color) and strongly in the near infrared, whereas deoxygenated hemoglobin has the opposite absorption. This fact is used in a "pulse oximeter" to measure oxygen saturation in arterial blood. The device clips onto the end of a person's finger and has two light-emitting diodes --a red (640 nm) and an infrared (965 nm)-- and a photocell that detects the amount of light transmitted through the finger at each wavelength. (a) Determine the frequency of each of these light sources. Red 4.6875e14 Correct: Your answer is correct. Hz Infrared 3.1088e14 Correct: Your answer is correct. Hz
(b) If 64% of the energy of the red source is absorbed in the blood, by what factor does the amplitude of the electromagnetic wave change? [Hint: The intensity of the wave is equal to the average power per unit area as given by the equation given below.] 21.97 Incorrect: Your answer is incorrect. Your response differs significantly from the correct answer. Rework your solution from the beginning and check each step carefully. I = (E_(max))^2)/(2mu_0c) = c/(2mu_0)B_((max))^2
how do you do part b?
Explanation / Answer
a) Frequency = speed of light / wavelength = 3x10^8 m/s / 640x10^-9m
= 4.688 x 1014 Hz
b) The energy transported by a wave is directly proportional to the square of the amplitude of the wave.
If 72% (0.72) is absorbed, the remainder is 0.28 so the amplitude is sqrt 0.28
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