[time-nuts] Measuring speed of light or reproducing a metre

Brian Alsop alsopb at nc.rr.com
Mon Jun 24 12:21:15 UTC 2013


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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