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 (638 nm) and an infrared (974 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.

Answer 1

Answer:

$4.70\cdot 10^{14} Hz, 3.08\cdot 10^{14} Hz$

Explanation:

The frequency of a light wave is given by:

$f=\frac{c}{\lambda}$

where

$c=3.0\cdot 10^8 m/s$ is the speed of light

$\lambda$ is the wavelength

For the red light emitted by the diode,

$\lambda = 638 nm=6.38\cdot 10^{-7}m$

So, the frequency is

$f=\frac{3.0\cdot 10^8 m/s}{6.38\cdot 10^{-7} m}=4.70\cdot 10^{14} Hz$

For the infrared light emitted by the diode,

$\lambda = 974 nm=9.74\cdot 10^{-7}m$

So, the frequency is

$f=\frac{3.0\cdot 10^8 m/s}{9.74\cdot 10^{-7} m}=3.08\cdot 10^{14} Hz$