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 (653 nm) and an infrared (935 nm)—and a photocell that detects the amount of light transmitted through the finger at each wavelength.

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?

Answer 1

Answer:

0.6

Explanation:

$I_i$ = Initial intensity

E denotes amplitude

Final intensity is

$I_f=(1-0.64)I_i=0.36I_i$

We have the relation

$\dfrac{E_i^2}{E_f^2}=\dfrac{I_i}{I_f}\\\Rightarrow \dfrac{E_i^2}{E_f^2}=\dfrac{I_f}{0.36I_i}\\\Rightarrow \dfrac{E_i^2}{E_f^2}=\dfrac{1}{0.36}\\\Rightarrow \dfrac{E_f^2}{E_i^2}=0.36\\\Rightarrow E_f^2=0.36E_i^2\\\Rightarrow E_f=0.6E_i$

The amplitude changes by a factor of 0.6