Short Title

Michelson Interferometer to Measure Index of Refraction of Air


Michelson Interferometer, index of refraction, air, optics

Subject Area

Physics, Laboratory

Type of Submission



Using a Michelson Interferometer, we experimentally measured the index of refraction of air, nair. We did so by constructing a plot of N versus ΔP/Patm, where N represents the number of fringe shifts in the interference pattern between two separated then recombined waves, and ΔP/Patm represents the ratio of the difference between our measured pressure readings of the gas evacuated out of a gas cell (ΔP) to atmospheric pressure (Patm). We then used the slope of the trend line to calculate nair. Our resulting value of nair was measured to be 1.000255 ± 0.000050, which was compared to the expected literature value of nair = 1.00029. This expected value falls within our calculated error. If the uncertainty is not included, then our percent error is equal to 0.004%.