Measuring the speed of light

ravisastry

Hi, how is the speed of light measured in objects such as water, glass, diamond etc ? what are the tools and techniques used. thanks in advance !

Hootenanny

Welcome to Physics Forums.

Just out of interest, why do you want to know? Why are you interested in the speed of light in transparent materials?

ravisastry

just wanted to know how speed of light is calculated in places other than vaccumm...who knows, the answer i get, might help in formulating some new theory !

Feldoh

In terms of materials a viable way would be interferometry

ravisastry

thanks...now, ill google "interferometry"

Hootenanny

I look forward to it.

stevenb

If you don't mind an indirect method, you can use Snell's law and measurent of refraction angles with oblique incidence. This should work well with the highly transparent materials you mentioned.

K^2

That's good for gases and fluids. Not so much for solid materials.

If you have a thick enough slab of material, and you send the beam through it a few times with mirrors, you can just time it directly.

One of the experiments done in the Intermediate Physics Lab in our department is measurement of speed of light using an oscilloscope, and LED, a photo-diode, and some mirrors. You basically use the oscilloscope to measure time it takes a pulse of light to travel a certain distance. You can get something like 10^-3 precision with that.

ravisastry

guys, im not getting what i was looking for "http://en.wikipedia.org/wiki/Interferometry" the link doesnt tell about speed of light measurement.
k^2 ... what i was looking for is, say you have a glass slab of 1 cm thickness. how much time would like to traverse this and roughly, how many atoms would it encounter. we can take any substance, not just glass. i'd like to know the time gap between a photon absorption and re-emission in any atom. do we have an experiment or ready made answer for my question :)

Danger

You might have to get into atomic physics or maybe even quantum mechanics in order to get your answer. I am over my head just by posting the foregoing, so I can be of no further help. Believe, though, that any reflection/refraction is a consequence of electron shell structure.

Vanadium 50

For solids you can use the Brewster angle. Kind of fun to measure the speed of light in coal.

Danger

That obviously brings to mind that there might be a new method of medical stool analysis to be patented here. Damn!, but I hate you!