c = 300000 km/s (n = 1)
ngheata = 1,31
nsticla = 1,5-1,62 (il luam a fi 1,56, adica la mijloc)
nvid = 1
===========================================
ngheata = c/v1 => v1 = c/ngheata = 300000 km/s/1,31 = 229007,63 km/s
nsticla = c/v2 => v2 = c/nsticla = 300000 km/s/1,56 = 192307,69 km/s
nvid = c/v3 => v3 = c/nvid = 300000 km/s/1 = 300000 km/s