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An experimentalist uses a Michelson interferometer to measure a wavelength of light emitted by neon atoms. She slowly moves mirror M2 until 10000 new bright central fringes have appeared. She then measures that the mirror has moved a distance of 3.164 mm. What is the wavelength of the light (in nm)?

1. 316.4
2. 632.8
3. 158.2
4. 1265.6

Correct answer: 632.8

Solution

When mirror M2 moves by d = 3.164 mm, the optical path difference changes by 2d. For N = 10000 fringes: lambda = 2d/N = 2 * 3.164 mm / 10000 = 6.328e-4 mm = 632.8 nm.

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