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Correct Answer: interference fringes
the key to measuring the speed of light by albert a. michelson was the use of interference fringes. this technique is grounded in the principles of wave interference, which occurs when two waves meet while traveling along the same medium. in the context of michelson's experiments, the waves in question were light waves.
michelson utilized an apparatus known as the michelson interferometer, which he initially developed with edward morley. this device split a beam of light into two parts, sending them along different paths and then recombining them. the core concept hinges on the fact that if the two beams travel exactly the same optical distance, they interfere constructively, but if the distances differ, they interfere destructively.
the interference fringes, which are the visible results of constructive and destructive interference, appear as bright and dark bands. by precisely measuring the positions of these fringes, michelson could determine how changes in path length affected the interference pattern. this measurement was crucial because the speed of light could be calculated by knowing how much one of the paths had to be adjusted to change the interference pattern.
in michelson's most famous experiment, the michelson-morley experiment, the goal was to detect the earth's motion through the "aether," which was then thought to be the medium through which light waves propagated. although the experiment is famous for its null result regarding the aether, the techniques developed proved instrumental in refining measurements of the speed of light.
thus, the clue that enabled michelson to measure the speed of light so accurately was the pattern of interference fringes. these fringes provided a sensitive indicator of changes in the path length of the light beams in his interferometer, allowing for precise calculations of light's speed based on how these lengths were manipulated during the experiments.
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