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Figure 2: Foucault's determination of the relative speed of light in air vs water. Light from a passing through a slit (not shown) is reflected by mirror m (rotating clockwise around c) towards the concave spherical mirrors M and M'. Lens L forms images of the slit on the surfaces of the two concave mirrors.
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).
For example, the speed of light in water is about 3/4 of that in vacuum. ... proposed a particle theory of light which was published posthumously in the 1660s.
[S 5]: 33 The overall speed of a beam of light should be a simple additive sum of its speed through the water plus the speed of the water. That is, if n is the index of refraction of water, so that c/n is the speed of light in stationary water, then the predicted speed of light w in one arm would be [S 2]: 40
The fact that light could be polarized was for the first time qualitatively explained by Newton using the particle theory. Étienne-Louis Malus in 1810 created a mathematical particle theory of polarization. Jean-Baptiste Biot in 1812 showed that this theory explained all known phenomena of light polarization. At that time polarization was ...
1905 – Albert Einstein publishes his special theory of relativity, including the mass–energy equivalence that would be later written as E = mc 2. 1906 – Alfred Bucherer introduces the name theory of relativity, based on Max Planck’s term relative theory.
Frequency dispersion of surface gravity waves on deep water. The red square moves with the phase velocity, and the green dots propagate with the group velocity. In this deep-water case, the phase velocity is twice the group velocity. The red square traverses the figure in the time it takes the green dot to traverse half.
For example, a beam of electrons can be diffracted just like a beam of light or a water wave. The concept that matter behaves like a wave was proposed by French physicist Louis de Broglie ( / d ə ˈ b r ɔɪ / ) in 1924, and so matter waves are also known as de Broglie waves .