Question

why is the definition of a metre related to the speed of light in vacuum?

Answer 1

Dear Student

The second and the speed of light are precisely defined, and the metre is then specified as a function of c and the second So when you experimentally measure the speed of light you are effectively measuring the length of the metre i.e. the experimental error is the error in the measurement of the metre not the error in the speed of light or the second. The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its value is exactly 299,792,458 metres per second, a figure that is exact because the length of the metre is defined from this constant and the international standard for time.