Physics Help Forum Fizeau rotating cogwheel

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 May 6th 2018, 01:51 PM #1 Banned   Join Date: Apr 2018 Posts: 92 Fizeau rotating cogwheel The first measurement of c that didn't make use of the heavens was by Armand Fizeau in 1849. He used a beam of light reflected from a mirror 8 km away. The beam was aimed at the teeth of a rapidly spinning wheel. The speed of the wheel was increased until its motion was such that the light's two-way passage coincided with a movement of the wheel's circumference by one tooth. This gave a value for c of 315,000 km/s. Leon Foucault improved on this result a year later using rotating mirrors, which gave the much more accurate value of 298,000 km/s. His technique was good enough to confirm that light travels slower in water than in air. ____________________________________ Fizeau (1848) attempts to measure the velocity of light using a light beam that is incident to a rotating cogwheel forming a pulsed light ray that propagates 8 km to a distance mirror and reflected back to the cogwheel. The time to form a single light pulse and the 16 km distance are used to calculate the velocity of light but a single light pulse cannot produce an intensity after propagating the distance of 16 km. Foucault (1850) replaced Fizeau's cogwheel with a rotating mirror but a single light pulse of Foucault's experiment also forms the same intensity problem as Fizeau's experiment. Are these the experiment that you are stating are used to verify the measurement of the velocity of light?
 May 6th 2018, 01:55 PM #2 Banned   Join Date: Apr 2018 Posts: 92 I do not think that it is physically possible to determine the velocity of light since the detection devices interfere with the measurement. Can anyone see this? And why do PHYSICISTs need so many different experiments to determine the velocity of light. It seems like they aren't quite sure of themselves. What do you think or do?
May 6th 2018, 03:58 PM   #3

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 Originally Posted by lovebunny I do not think that it is physically possible to determine the velocity of light since the detection devices interfere with the measurement. Can anyone see this? And why do PHYSICISTs need so many different experiments to determine the velocity of light. It seems like they aren't quite sure of themselves. What do you think or do?
Just because you think it can't be done doesn't mean it can't be done. As I said before even I have done it. (Using a rotation mirror.)

-Dan
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