Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Different ways to measure the speed of light experimentally ?

  1. Jan 25, 2009 #1
    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,
  2. jcsd
  3. Jan 26, 2009 #2


    User Avatar
    Homework Helper

    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 travelled 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.
  4. Jan 28, 2009 #3
    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 !

  5. Nov 21, 2010 #4
    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??
  6. Nov 21, 2010 #5


    User Avatar
    Homework Helper
    Gold Member

    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook