# Fizeau's Exp: Calculating Speed of Light w/ Red Laser

• Kryptuniite
In summary, Angular speed of the 8 gap wheel is variable. Red Laser (wavelength around 656.6 nm) has an approximate length of 1.5 meters. The speed of light is approximated to be 299,792,458 meters per second.
Kryptuniite

## Homework Statement

Angular Speed of the 8 gap wheel Is variable.
Red Laser (wavelength around 656.6 nm)
Approximate the length of the traveling ray to the mirror in meters.
Using the length of the traveling ray, calculate the speed of light.

c=lambda*f

## The Attempt at a Solution

I tried using a simple speed * time * distance equation but it didn't make sense to me.
I have looked for other similar threads but they are all dealing with different variables like finding out the perfect timing ect.

I think there is something missing in the problem statement.
Kryptuniite said:
speed * time * distance equation
I don't think there is any equation where you multiply those three things. Can you show what you actually did?

Here is the experiment and all of the data that has been given, when I click start the wheel then begins to turn and cut out the laser as it should in the experiment. Our professor asked us to find the length of the laser and I'm not quite sure how to solve that. Any information or tips would help!
( the distance to from the wheel to the mirror is 8.65km)

Thanks MFB!

#### Attachments

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It's too bad that only a thumbnail was uploaded. I can no more read what's written in this image than I can use my sun glasses to see through walls.

In any event, have you read up on how Fizeau set up his apparatus and used it to calculate his value of the speed of light?

Yes I have watched many videos on how he set it up and found his value for the speed of light. I am just unsure about the part where we have to calculate the distance of the laser ray.

You'll need the angular velocity of the wheel or something similar to find the distance.

The sketch seems to have a length given there, which would make finding the length a bit pointless.

In the lab the angular velocity is actually variable to our choosing, and for the length that we are trying to find is actually the length of the laser that has been let in by the turning of the wheel.

Sorry if there was any confusion.

Sure, for an actual setup you measure the distance, but as far as I understood you are supposed to calculate it here based on other given quantities. But then you need the angular velocity of the wheel.

Okay thanks! Any idea on formulas to use with the angular velocity to find the distance? Or where to look for them at?

Speed is distance traveled divided by time needed, as simple as that.
The time depends on the angular velocity and the number of holes in the wheel.

## 1. What is Fizeau's Experiment and why is it important in calculating the speed of light?

Fizeau's Experiment is an experiment conducted in the 19th century by French physicist Armand Fizeau to determine the speed of light. It involves using a rotating wheel with evenly spaced teeth and a beam of light to measure the speed of light. This experiment is important because it provided a more accurate measurement of the speed of light, which revolutionized our understanding of physics and paved the way for further scientific discoveries.

## 2. What was the outcome of Fizeau's Experiment?

Fizeau's Experiment resulted in a measurement of the speed of light that was within 5% of the currently accepted value. This confirmed that the speed of light is a constant and provided a more precise measurement than previous experiments.

## 3. How does Fizeau's Experiment work?

In Fizeau's Experiment, a beam of light is directed at a toothed wheel that is rotating at a known speed. The light passes through the gaps between the teeth and reflects off a mirror placed a certain distance away. By measuring the time it takes for the light to travel back and forth between the wheel and the mirror, the speed of light can be calculated using the known distance and rotation speed of the wheel.

## 4. What are some limitations of Fizeau's Experiment?

One limitation of Fizeau's Experiment is that it assumes the speed of light is constant in all mediums. However, we now know that the speed of light can vary in different mediums. Another limitation is that the experiment relies on precise measurements of distance and rotation speed, which can be difficult to obtain accurately. Additionally, the experiment does not account for other factors that may affect the speed of light, such as gravitational fields.

## 5. How has Fizeau's Experiment influenced modern science?

Fizeau's Experiment has had a significant impact on modern science by providing a more accurate measurement of the speed of light, which is a fundamental constant in physics. This experiment has also led to further studies and theories about the nature of light and its behavior in different mediums. Additionally, the principles of Fizeau's Experiment have been applied to other areas of science, such as astronomy, to measure the speed of objects in space.

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