The time issue was effectively eliminated by the Michaelson-Morley
interferometer. One used a monochromatic light and an array of mirrors
which split the light in opposite directions around the track. The two
beams were recombined and an interference pattern resulted. One counted
the number interference fringes passing by while moving one mirror in
one path.
Knowing the number of fringes, wavelength of light and the mirror
movement, one could compute c.
http://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment
Actually used one of these in a physics lab in about 1962. Produces a
quite reasonable estimate of c. Other methods could be used to
accurately know the wavelength of light.
The other experiments to measure the gravitational constant G were
equally interesting.
The real reason for the interferometer was to try and detect the effect
of the "aether" which light was supposedly propagated in. To everyone's
surprise, there was no detectable "aether".
Brian
On 6/24/2013 11:26, Jim Lux wrote:
On 6/23/13 10:48 PM, DaveH wrote:
Something a bit similar was first published by Nick Hood in 2007.
Here is a copy:
http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p056.
shtml
Here is Nick's website:
http://cullaloe.com/
Some people use marshmallows.
Dave
the only problem is that you don't have a very accurate measurement of
the microwave oven frequency and the mode pattern isn't very "sharp". So
this might get you 1 sig fig. Granted, most folks only use 1 sig fig 3E8
m/sec, but that's just a happenstance since c happens to be close to a
round number.
And that gets back to another time-nuts kind of question..
How accurately can you measure length and time? (in a science demo sort
of way.. without getting a Rb or GPSDO, etc.) For most school age kids,
the sources of time available are fairly lengthy (e.g. 1 second ticks
from wwv by phone, stopwatches built into iphones, etc.)
Tape measures and meter sticks are readily available.
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