Question

A "pulse oximeter" operates by using light and a photocelltomeasure oxygen saturation in arterial blood. The transmissionoflight energy as it passes through a solution oflight-absorbingmolecules is described by the Beer-Lambert law,given below, whichgives the decrease in intensity I in terms of thedistance L thelight has traveled through a fluid with aconcentration C of thelight-absorbing molecule.

I =I₀10^-εCLorlog₁₀(I / I₀)=-εCL

The quantity ε is called the extinctioncoefficient, andits value depends on the frequency of the light.(It has units ofm²/mol.) Assume that the extinctioncoefficient for 660nm light passing through a solution ofoxygenated hemoglobin isidentical to the coefficient for 940 nmlight passing throughdeoxygenated hemoglobin. Assume also that 940nm light has zeroabsorption (ε = 0) inoxygenated hemoglobin and 660 nmlight has zero absorption indeoxygenated hemoglobin. If 31% oftheenergy of the red source and 78% of theinfrared energy istransmitted through the blood, determine thefraction of hemoglobinthat is oxygenated.

Your response is within 10% of the correctvalue. This may be due toroundoff error, or you could have amistake in your calculation.Carry out all intermediate results toat least four-digit accuracyto minimize roundofferror.%

I was usingthis as a guide but I get the same answer anditswrong:/answers-mar-09/physics/urgent-need-help-please-a-pulse-oximeter-operates-by-using-light-and-a-photocell-to_514319.aspx