1. The problem statement, all variables and given/known data "Calculate the reflection loss when a beam of radiant energy passes through an empty quartz cell assuming the refractive index of quartz is 1.55" 2. Relevant equations I/I_i = ((n2-n1) / (n2+n1))^2 3. The attempt at a solution I'm taking the refractive index through the empty cell to be 1 (is that right?) I/I_i = ((n2-n1) / (n2+n1))^2 = ((1.55-1)/(1.55+1))^2 = 0.047 or 4.7% The answer in the back of the book is 17.3 % what am i doing wrong?