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How was Dorsey able to measure speed of light with 3 significant digits in the year of 1907?

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How does en.wikipedia.org/wiki/Speed_of_light#Electromagnetic_constants fail to answer the question? –  dmckee May 12 '12 at 14:44

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They just had to measure the capacitance of a capacitor!

If you can build a precise dimensioned capacitor you can work out it's capacitance with an equation including the vacuum permittivity ($ε_0$). It's easy to build the dimensions of the metal plates in a capacitor to high accuracy, and you can measure current accurately so by measuring the capacitance you get an experimental value for this constant.

Then you get a value of $c$ from $c^2 = 1/(ε_0μ_0)$
$μ_0$ is fixed by definition of the electrical units you are using.

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