calculating the speed of light?

Question

i used a duel oscilloscope,
which was set to :
2.0 × 10^-8 seconds per center meter,
the light path i created was 4112cm, in length, the difference on the dual oscilloscope was 3.1cm, (peek to peek)


how do i from there calculate the speed of light?
(top answer goes to best explained)


so far i did 3.1(2.0 × 10^-8) = 6.2 x 10^-8
then speed= distance divided by time taken(unit given in how much you want the answer unit to be)
4112/6.2 x 10^-8 = ~ 6.632258 x 10^10, which i know is way over the speed of light, were have i gone wrong?

Answer 1

Well, actually, the speed of light is 2.99792458 x 10^10 cm / sec, so you're off by a factor of roughly 2.21. I'm not sure about the experimental setup you have for the measurement of the speed of light, but I suspect that either you've got the distance twice as far as it's supposed to be, or you've got the time half of what it's supposed to be. For example, if the peaks appear to be more like square waves, you're supposed to measure the between the first corners of both waves, not the width of the valley between. For another example, if you are using a partially silvered mirror to direct the first pulse to the detector, then it's the DIFFERENCE between the 2 light paths that you divide by the difference in time. Without knowing exactly how you've set up your apparatus, I can only guess what could be your problem.

Answer 2

I thought the speed of light was like 186,000 mi/h. Or maybe that's the speed of sound.