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Question
Consider Galileo's method of measuring the speed of light using two lanterns. To get an accuracy of about 10%, the time taken by the experimenter in closing or opening the shutter should be about one tenth of the time taken by the light in going from one experimenter to the other. Assume that it takes 1/100 second for an experimenter to close or open the shutter. How far should the two experimenters be to get a 10% accuracy? What are the difficulties in having this separation?
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Solution
We have speed of light = 299792458 m/s
To have a accuracy of 10% the light has to travel 1/10th of a second between the observers so,
Distance travelled by the light in 0.1 s = 0.1×299792458= 29979 km.
The difficulty in separation of that distance will be the curvature of earth. As the earth’s surface is curved, light from one of the experimenters won’t reach the other.
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