Oxygenated hemoglobin absorbs weakly in the red hence its re

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?

Solution

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