You are using a hydrogen discharge tube and high quality red and blue light filters as the light source for a Michelson interfer

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You are using a hydrogen discharge tube and high quality red and blue light filters as the light source for a Michelson interfer

ometer. The hydrogen discharge tube provides light of several different wavelengths (colors) in the visible range. The red light in the hydrogen spectrum has a wavelength of 656.3 nm and the blue light has a wavelength of 434.0 nm. When using the discharge tube and the red filter as the light source, you view a bright red spot in the viewing area of the interferometer. You now move the movable mirror away from the beam splitter and observe 158 bright spots. You replace the red filter with the blue filter and observe a bright blue spot in the interferometer. You now move the movable mirror towards the beam splitter and observe 114 bright spots. Determine the final displacement (include sign) of the moveable mirror. (Assume the positive direction is away from the beam splitter.)

Physics

1 answer:

Keith_Richards [3.2K] · Answer 1 · 2026-04-09T07:52:40+03:00

Final displacement equals +24484.5 nm. The path difference observed with red light (λ1 = 656.3 nm) with 158 bright spots can be represented as: Δr = 2d2 - 2d1 = 150λ1, leading to the equation 2d2 - 2d1 = 150λ1. Dividing both sides results in: d2 - d1 = 75λ1 - - - - eq1, with d1 being the distance from the beam splitter to the fixed mirror, and d2 indicating the position of the movable mirror when 158 bright spots appear. Then, with 114 bright spots, the path difference is Δr = 2d'2 - 2d1 = 114λ1, simplifying to 2d'2 - 2d1 = 114λ1. Subsequent division gives: d'2 - d1 = 57λ1, where d'2 is the revised position of the movable mirror. The displacement of the movable mirror, (d2 - d'2), can be calculated by subtracting eq2 from eq1, leading to: d2 - d'2 = 75λ1 - 57λ2, with λ1 equal to 656.3 nm and λ2 equal to 434.0 nm. Finally, this gives d2 - d'2 = 75(656.3) - 57(434), resulting in +24484.5 nm.