Calculating c from Fizeau's experiment? (AQA Turning Points)

I think I conceptually understand Fizeau's experiement but am really stuck on the calculation aspect. Image 17-03-2025 at 18.33.jpeg

I'm not even sure where to start. I thought about working out the time period from the angular velocity but I'm not sure which value to use? Why does the number of notches matter?

Reply 1

Nitrotoluene

Original post by nwar

I think I conceptually understand Fizeau's experiement but am really stuck on the calculation aspect. Image 17-03-2025 at 18.33.jpeg

I'm not even sure where to start. I thought about working out the time period from the angular velocity but I'm not sure which value to use? Why does the number of notches matter?

In my time, in my second part physics course, I used the following formula:

V = 2xdxNxf

where velocity = 2 x distance between mirrors x number of teeth on wheel x frequency
Right, so for light to get through, the time it takes to bounce off the mirror must equal the time it takes for the next "tooth" (or slot) to get to the same spot. So, treat Nxf as the frequency in which these slots coincide. So 1/(Nxf) is the period of that. If any light does make it through, it travels 2xd in one period; therefore, the total distance it covers (per second) is 2xdxNxf.
Kind regards from Italy,
Sandro

Reply 2

Drummy

Original post by nwar

I think I conceptually understand Fizeau's experiement but am really stuck on the calculation aspect. Image 17-03-2025 at 18.33.jpeg

I'm not even sure where to start. I thought about working out the time period from the angular velocity but I'm not sure which value to use? Why does the number of notches matter?

so the time it takes for light to get from the wheel to the mirror and back is the time it takes for the wheel to rotate by one notch (for the 25.2 revs per second)

Reply 3

nwar

Study Forum Helper

Original post by Nitrotoluene

In my time, in my second part physics course, I used the following formula:

V = 2xdxNxf

Thank you so much Sandro!

Reply 4

nwar

Study Forum Helper

Original post by Drummy

so the time it takes for light to get from the wheel to the mirror and back is the time it takes for the wheel to rotate by one notch (for the 25.2 revs per second)