Different ways to measure the speed of light experimentally ?

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Discussion Overview

The discussion revolves around various experimental methods to measure the speed of light. Participants share their experiences and seek additional techniques, focusing on practical approaches suitable for projects and public demonstrations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • ATH500 inquires about simple methods to measure the speed of light, mentioning a microwave method as a starting point.
  • One participant describes a complex method involving a spinning mirror and a continuous laser, noting the challenges faced during the measurement.
  • Another participant shares a method using a homemade tunable dye laser and an oscilloscope to measure the speed of light based on pulse separation.
  • ATH500 plans to use LEDs and fiber optics with an oscilloscope to measure the speed of light and seeks further suggestions.
  • A participant expresses interest in conducting a public event experiment using lasers and mirrors, asking for advice on creating a DIY oscilloscope or simple electronic circuit for measurement.
  • ATH500 reiterates the need for multiple methods and raises a concern about the measurement of microwave frequency in relation to the microwave method.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best methods, and multiple competing views and techniques are presented without resolution.

Contextual Notes

Some methods discussed involve complex setups and equipment, while others seek simpler approaches. There are concerns about the accuracy of measurements related to frequency determination.

Who May Find This Useful

Individuals interested in experimental physics, educators looking for demonstration ideas, and students working on projects related to the speed of light.

ATH500
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Hello,
I would like to know different ways to measure the speed of light. It's for one of my project. I would like to know if there are simple ways to do it. I already know that we can measure the speed of light using a microwave: http://orbitingfrog.com/blog/2008/05/13/measure-the-speed-of-light-using-your-microwave/

This seems like the easiest way to do it for me right now but I need to use more than one way to measure it in order to compare different data experimentally and find the best results. I would need easy ways to calculate the speed of light. Do you know any other methods ?

Thank you,
ATH500
 
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I first measured the speed of light in a 4th year lab - using the spinning mirror and a continuous laser. It was NOT easy!

The second time, I was building lasers at York U in Toronto about 1975. My home made tunable dye laser happened to have a pulse duration of about 1 nanosecond. I also had an expensive HP oscilloscope that could show that pulse cleanly from a photocell. Measuring the speed of light was as simple as splitting the beam with a glass slide so part of it traveled a bit further, say a meter extra, and two pulses appeared on the scope separated by 3 nanoseconds. So the speed of light was 1 m divided by 3 nanoseconds.
 
Thanks for your answer,
I have access to all the equipment I need to measure the speed of light with an oscilloscope. I'll use two LEDS connected to fiber optics cable of different length and generate two squared signal using a photodiode connected to a circuit and the oscilloscope.

Thank you !

If anybody has any other suggestions to measure the speed of light, please tell me !

ATH500
 
I am doing a public event soon involving taking night images from elevations to celebrate equinox. As part of making the event more fun, I wanted to include a simple physics experiment to measure the speed of light. I have lasers, and mirrors and want to use them over distance. I don't have an oscilloscope but I have a lap-top if there's a cheap way to turn one into one. I also have various kinds of photo detectors I can hookup. Is there a way to make the laptop a cheap DIY oscilloscope or a simple electronic circuit I can design to measure the speed with and output some useful readable info with LEDS or some other way??
 
ATH500 said:
Hello,
I would like to know different ways to measure the speed of light. It's for one of my project. I would like to know if there are simple ways to do it. I already know that we can measure the speed of light using a microwave: http://orbitingfrog.com/blog/2008/05/13/measure-the-speed-of-light-using-your-microwave/

This seems like the easiest way to do it for me right now but I need to use more than one way to measure it in order to compare different data experimentally and find the best results. I would need easy ways to calculate the speed of light. Do you know any other methods ?

Thank you,
ATH500

I saw this or similar from an enthusiastic Science presenter who is having some success for this and similar it on British TV recently.

Shouldn't one feel uneasy until one knows how the frequency of the microwave is known or can be measured? I do.
 

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