GATE 2021 IN – Question 32
A Michelson interferometer’s movable arm is displaced 325 μm in vacuum (n = 1), and 1000 fringes cross the observation point. The laser wavelength is ______ nm.
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: 650 to 650
Explanation
Moving one mirror by d changes round-trip optical path by 2d. N fringes therefore satisfy Nλ=2d. With d=325 μm and N=1000, λ=650 μm/1000=**650 nm**.