1. The problem statement, all variables and given/known data A light ray enters the atmosphere of the Earth and descends vertically to the surface a distance h = 101.2-km below. The index of refraction where the light enters the atmosphere is n = 1.00 and it increases linearly with distance to a value of n= 1.000293 at the Earth's surface. Over what time interval does the light traverse this path? 2. Relevant equations v1/v2=n2/n1 v1=3e8 n1=1 v2=3e8/n2 D=distance from atmosphere barrier 3. The attempt at a solution So the increase in n2 per m = 1/345392491 Therefore n2=(D/345392491) +1 v2=3e8/(1+(D/345392491)) So v2 changes with distance. I'm not sure where to go from here to get time.