Albert A. Michelson very carefully measured the speed of light using an alternat

Question

Albert A. Michelson very carefully measured the speed of light using an alternative version of the technique developed by Fizeau. Light was reflected from one face of a rotating eight-sided mirror toward a stationary mirror 36.5 km away. At certain rates of rotation, the returning beam of light was directed towardthe eye of an observer as shown.

What minimum angular speed must the rotating mirror have in order that side A will
have rotated to position B, causing the light to be reflected to the eye? Answer in units of rev/s

What is the next-higher angular velocity that will enable the source of light to be seen? Answer in units of rev/s

Explanation / Answer

It will take light (2 * 36.5 km)/(299790 km/s) = 2.435 * 10-4 sec to make the round trip.

We want the rotating mirror to make 1/8 of a turn in that time, so its rotation speed would have to be 1/(8 * 2.435 * 10-4) = 513.3 rev/s.

If it rotated twice as fast that would be the next speed that would match: 1026.6 rev/s

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