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The Conférence Générale des Poids et Mésures (1983) defined the meter to be "the length of the path travelled by light in a vacuum during a time interval of 1/299792458 of a second". This sets the speed of light to be c = 299792458 m s−1 exactly.

The simplest propagating sinusoidal wave may be written in the form A = A0 cos (kx − ωt), where A0 is the amplitude. The term in the bracket is the phase of the wave, x and t being position and time. Thus, a surface of constant phase propagates with the phase velocity v = ω/k, where ω = 2πf is the angular frequency for frequency f and k = 2π/λ is the Wave Number for wavelength λ. In a vacuum v = c. Otherwise v = c/m, where m is the Refractive Index. The phase velocity may be measured by Interferometry.

REFERENCES

Born, M. and Wolf, E. (1980) Principles of Optics, 6th edn., Pergamon Press, Oxford.

References

  1. Born, M. and Wolf, E. (1980) Principles of Optics, 6th edn., Pergamon Press, Oxford.
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