Light propagate faster through medium “a” than medium “b”
1. which of the medium had more optical density
2. state the condition at which no change in direction of propagation of path of light ray would take place when it passes through medium “a” to “b”

Amichelson interferometer operating at a 600 nm wavelength has a 3.02-cm-long glass cell in one arm. to begin, the air is pumped out of the cell and mirror m2 is adjusted to produce a bright spot at the center of the interference pattern. then a valve is opened and air is slowly admitted into the cell. the index of refraction of air at 1.00 atm pressure is 1.00028.how many bright-dark-bright fringe shifts are observed as the cell fills with air?