Oxygenated hemoglobin absorbs weakly in the red (hence its red color) and strong

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 (645 nm) and an infrared (940 nm) - and a photocell that detects the amount of light transmitted through the finger at each wavelength. Determine the frequency of each of these light sources. If 62% of the energy of the red source is absorbed in the blood, by what factor does the amplitude of the electromagnetic wave change? I = E_max^2 / 2 mu_0c = c / 2 mu_0 B_max^2

Explanation / Answer

Given that

The wavelength of the red light (lamdared) =645nm =645*10-9m

The wavelgnth of the infrared light (lamdainfrared) =940nm=940*10-9m

Speed of the light (c) =3*108m/s

The frequency of each light source given by f =c/lamda

Now the requency of the red light fred =c/lamdared =3*108m/s/645*10-9m =4.65*1014Hz

and the frequency of the infrared light  =c/lamdared =3*108m/s/940*10-9m =3.19*1014Hz

We know that

I directly proportional to E2rms

Incidnet intensity =Ii

and final intensity (If) =(100%-62%)Ii

From the equation we have

Emaxi/Emaf =Sqrt(If/Ii)

=Sqrt(0.38Ii/Ii)

=Sqrt(0.38)

=0.616

Therefore the electromagnetic wave changes by a factor of 0.616

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