RI using Michelson Interferometer, help please

  • Thread starter Rocksicle
  • Start date


I'm doing a college project, and part of it involves finding the refractive index of a microscope cover slip. I am using a Michelson Interferometer, but the handbook for it is really badly written and coming to pieces, so I am a bit lost.

This is what I have got so far:
Used a cover slip, of thickness 0.19mm.
White bar’s position at start = 15.75
With cover slip 1, white bar = 15.27
With cover slip 2, white bar = 15.26
With cover slip 3, white bar =15.27

The interferometer was set up and green light shone into it with a simple desk lamp that had a green filter attached. By moving the mirror and looking through the viewfinder, the central lines were found. These are the most sharp and least curved. The very middle line was where measurements would be taken from, and fortunately it was easily distinguishable from its peers so it could be found again. The reading for this mirror displacement was taken so it could be compared with later ones.

Then a cover slip was affixed in the light pathway, and the same central white band found in the viewfinder. The mirror displacement needed for this was noted. This process was repeated twice more with two new cover slips to help avoid error, but they seem fairly uniform as the results were so similar (less than 0.001% difference).

These measurements are off by a factor of 5, however, because the scale on the XXXX does not take into account the lever between it and the mirror. This said, the new figures for mirror displacement are:

Cover slip: Displacement from 0 (mm):
No cover slip 15.75 x 5 = 78.75
Cover slip 1 15.27 x 5 = 76.35
Cover slip 2 15.26 x 5 = 76.30
Cover slip 3 15.27 x 5 = 76.35

The refractive index can be calculated using the formula:
R = V1 / V2
Where R is the refractive index, V1 is the speed of light in a vacuum and V2 is the speed of light in the object.
All that may or may not make much sense, but I what I really need to know is how to use my measurements to find the RI of this glass.

I know I could ask the manufacturer, but that is not allowed as part of the project.

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