Fizeau's Experiment for Speed of Light Flashcards
(6 cards)
What basic setup did Fizeau use to measure the speed of light?
A pulsed beam of light was passed through a gap in a rotating toothed wheel, reflected off a distant mirror, and returned back through the same gap — unless a tooth blocked it due to the wheel’s rotation.
What happens when the rotation speed of the wheel increases during Fizeau’s experiment?
At a certain speed, the returning light is blocked by the next tooth, making the beam no longer visible. If the speed is doubled, the light passes through the next gap and becomes visible again.
How does the toothed wheel work in terms of time intervals?
If the wheel has n teeth and n gaps, then after half a revolution a tooth replaces a gap. So, a tooth replaces a gap every:
1/(2nf) seconds
where f is the rotation frequency of the wheel.
How can the time for the light’s round trip be calculated in Fizeau’s method?
The round trip time (to the mirror and back) is equal to the time between a gap and the next tooth:
t = 1/(2nf)
What formula did Fizeau use to calculate the speed of light?
If d is the distance from the wheel to the mirror, then:
Speed of light, c = 2d/t = 4dnf
Why was Fizeau’s experiment historically significant?
Fizeau’s measured value of c was very close to Maxwell’s predicted value, providing strong experimental evidence that light is an electromagnetic wave.
