100 lumen of light are incident on an interface which has 25% reflectance. At a point 3cm into the new medium, the amount of transmitted light is measured as 50 lumen. What is the absorptance of the material per cm?

Question

100 lumen of light are incident on an interface which has 25% reflectance.  At a point 3cm into the new medium, the amount of transmitted light is measured as 50 lumen.  What is the absorptance of the material per cm?

drwls · Answer

0.75 * exp(-k*L) = 50/100 = 0.5 L = 3 cm The 0.75 is the fraction that penetrates the surface. Solve for k exp(-kL) = 0.667 kL = 0.4055 k = 0.135 cm^-1