Question
The Michelson interferometer can be used to measure an index of refraction of a gas by placing the evacuated transparent tube in the light path along one arm of the device. Fringe shifts occur as the gas is slowly added to the tube.
In this problem one fringe shift is distinct to mean from a bright pattern to the next dark pattern and not bright to dark and back again to a bright that would be two fringe shifts.
These fringe shifts occur since wave- length of the light changes inside the gas filled tube.
Suppose that 658 nm light is used, the tube is 2.79 cm long, and that 119 fringe shifts occur as the pressure of the gas in tube increases to atmospheric pressure.
Compute n gas, the index of refraction of the gas.
The answer should be within ± 0.001%