Set 17 Problem 3 to mirror M1 Glass container Source- Ms M2 d One of the beams of an interferometer passes through a small glass cell containing a cavity d = 1.36 cm long. When a gas is allowed to slowly fill the container, a total of 186 dark fringes are counted to move past a reference line. The light used has a wavelength in vacuum of 623 nm. Calculate the index of refraction of the gas at its final density, assuming that the interferometer is in vacuum. Give your answer as An = gas - vacuum = gas - 1 (since vacuum is exactly one by definition.) An = abc sin(x x10 Submit Reset Reset All There must be 186 additional wavelengths that fit in the effective length of the gas-filled cell than fit in the cell when it was evacuated. How is the wavelength in gas related to the wavelength in vacuum? The light passes through the gas-filled cell twice, so its effective length is twice its actual length