 Solution

ID: past-exam-of-the-physics-course-of-the-year-4-of-the-natural-sciences-course-of-the-university-of-cambridge/2014/paper-1/a5/solution

Moving one Michelson mirror changes optical path difference by twice its displacement. Therefore

2 d = 10 λ, d = 2.50 μ m .

For two-wavelength Michelson rephasing, start from a position where both colours are bright: the next simultaneous bright centre requires

2Δ d

to be a common integer multiple of both wavelengths. The smallest is

6 (500 nm) = 5 (600 nm) = 3.00 μ m

, giving an additional mirror movement of $1.50 μ m$ .

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