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  2. Speed of light - Wikipedia

    en.wikipedia.org/wiki/Speed_of_Light

    The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour).

  3. Electromagnetic wave equation - Wikipedia

    en.wikipedia.org/wiki/Electromagnetic_wave_equation

    is the speed of light (i.e. phase velocity) in a medium with permeability μ, and permittivity ε, and ∇ 2 is the Laplace operator. In a vacuum, v ph = c 0 = 299 792 458 m/s, a fundamental physical constant. [1] The electromagnetic wave equation derives from Maxwell's equations.

  4. One-way speed of light - Wikipedia

    en.wikipedia.org/wiki/One-way_speed_of_light

    The two-way speed of light is the average speed of light from one point, such as a source, to a mirror and back again. Because the light starts and finishes in the same place, only one clock is needed to measure the total time; thus, this speed can be experimentally determined independently of any clock synchronization scheme.

  5. Refractive index - Wikipedia

    en.wikipedia.org/wiki/Refractive_index

    As shown in the Fizeau experiment, when light is transmitted through a moving medium, its speed relative to an observer traveling with speed v in the same direction as the light is: = + + + (). The momentum of photons in a medium of refractive index n is a complex and controversial issue with two different values having different physical ...

  6. Michelson–Morley experiment - Wikipedia

    en.wikipedia.org/wiki/Michelson–Morley_experiment

    For instance, the Fizeau wheel could measure the speed of light to perhaps 5% accuracy, which was quite inadequate for measuring directly a first-order 0.01% change in the speed of light. A number of physicists therefore attempted to make measurements of indirect first-order effects not of the speed of light itself, but of variations in the ...

  7. Light - Wikipedia

    en.wikipedia.org/wiki/Light

    The speed of light in vacuum is defined to be exactly 299 792 458 m/s (approximately 186,282 miles per second). The fixed value of the speed of light in SI units results from the fact that the metre is now defined in terms of the speed of light. All forms of electromagnetic radiation move at exactly this same speed in vacuum.

  8. Speed of gravity - Wikipedia

    en.wikipedia.org/wiki/Speed_of_gravity

    Formally, c is a conversion factor for changing the unit of time to the unit of space. [4] This makes it the only speed which does not depend either on the motion of an observer or a source of light and / or gravity. Thus, the speed of "light" is also the speed of gravitational waves, and further the speed of any massless particle.

  9. Fizeau's measurement of the speed of light in air - Wikipedia

    en.wikipedia.org/wiki/Fizeau's_measurement_of_the...

    At 3 times the speed it was again eclipsed. [3] [4] Given the rotational speed of the wheel and the distance between the wheel and the mirror, Fizeau was able to calculate a value of 2 × 8633m × 720 × 25.2/s = 313,274,304 m/s for the speed of light. Fizeau's value for the speed of light was 4.5% too high. [5] The correct value is 299,792,458 ...