Oxygenated hemoglobin absorbs weakly in the red (hence its red color) and strong
ID: 1606516 • Letter: O
Question
Oxygenated hemoglobin absorbs weakly in the red (hence its red color) and strongly in the near infrared, while 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 (675 nm) and an infrared (955 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.
(b) If 63% 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 Equation 21.28 given below.]
Explanation / Answer
a) lambda(red) = 675 nm ; lambda(infrared) = 955 nm
we know that, c = f lambda => f = c/lambda
f(red) = c/lambda(red)
f(red) = 3 x 10^8/(675 x 10^-9) = 4.44 x 10^14 Hz
f(infrared) = c/lambda(indrared)
f(infrared) = 3 x 10^8/(955 x 10^-9) = 3.14 x 10^14 Hz
Hence, f(red) = 4.44 x 10^14 Hz and f(infrared) = 3.14 x 10^14 Hz
b)63% = 0.63 of the total is absorbed, remiander is:
r = 1 - 0.63 = 0.37
So the factor by which the amplitude change will be:
f = sqrt (0.37) = 0.6083
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.