1. The problem statement, all variables and given/known data What is the phase velocity of light in glass if n=1.5 at λ=500nm 2. Relevant equations n=c/vp =λ0/λ 3. The attempt at a solution 1.5 = (3x10^8) / vp vp = (3x10^8)/1.5 I'm not entirely sure if the equation I have used is the correct one. It does not use the λ=500nm as given in the question.