Question

In one arm of a Michelson interferometer, a flame is placed below one of the arms which heats the air and changes its index of refraction. As the air heats up, 5 interference fringes (m = 5) are observed while using a laser of wavelength 650 nm. If the index of refraction of room temperature air is 1.00029, what is the index of refraction of hot air? Assume the flame diameter is 3 mm.

Answer 1

The number of fringes in vacuum (No) are given by,

The number of fringes observed when the medium is room temperature air is,

Similary, the number of fringes observed when the medium is heated is,

So, the shift in the fringes when the medium is heated is,

So, the RI of hot air is 0.99975.

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