Figure shows the apparatus used by Armand H. L. Fizeau (1819€“1896) to measure the speed of light. The basic idea is to measure the total time it takes light to travel from some point to a distant mirror and back. If d is the distance between the light source and the mirror, and if the transit time for one round-trip is t, then the speed of light is c = 2d/t. To measure the transit time, Fizeau used a rotating toothed wheel, which converts an otherwise continuous beam of light to a series of light pulses. The rotation of the wheel controls what an observer at the light source sees. For example, assume that the toothed wheel of the Fizeau experiment has 360 teeth and is rotating at a speed of 27.5 rev/s when the light from the source is extinguished€”that is, when a burst of light passing through opening A in Figure is blocked by tooth B on return. If the distance to the mirror is 7 500 m, find the speed oflight.

Transcribed Image Text:

AB Toothed wheel Mirror