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

0.6

Step-by-step 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

`(E_i^2)/(E_f^2)=(I_i)/(I_f)\\\Rightarrow (E_i^2)/(E_f^2)=(I_f)/(0.36I_i)\\\Rightarrow (E_i^2)/(E_f^2)=(1)/(0.36)\\\Rightarrow (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