Speed of light in vacuum in the context of Invariant (physics)

⭐ Core Definition: Speed of light in vacuum

The speed of light in vacuum, often called simply speed of light and commonly denoted $c$ , is a universal physical constant exactly equal to 299,792,458 metres per second (approximately 1 billion kilometres per hour; 700 million miles per hour). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1⁄299792458 second. The speed of light is the same for all observers, no matter their relative velocity. It is the upper limit for the speed at which information, matter, or energy can travel through space.

All forms of electromagnetic radiation, including visible light, travel in vacuum at the speed c. For many practical purposes, light and other electromagnetic waves will appear to propagate instantaneously, but for long distances and sensitive measurements, their finite speed has noticeable effects. Much starlight viewed on Earth is from the distant past, allowing humans to study the history of the universe by viewing distant objects. When communicating with distant space probes, it can take hours for signals to travel. In computing, the speed of light fixes the ultimate minimum communication delay. The speed of light can be used in time of flight measurements to measure large distances to extremely high precision.

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Speed of light in vacuum in the context of Refractive index

In optics, the refractive index (also called refraction index or index of refraction), often denoted n, is the ratio of the speed of light in vacuum (c) to the speed of light in a given optical medium (v), $n = c / v$ . The refractive index determines how much the path of light is bent, or refracted, when entering a material, as described by Snell's law of refraction, $n 1 sin θ 1 = n 2 sin θ 2$ , where $θ 1$ and $θ 2$ are the angle of incidence and angle of refraction, respectively, of a ray crossing the interface between two media with refractive indices $n 1$ and $n 2$ . The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the critical angle for total internal reflection, their intensity (Fresnel equations) and Brewster's angle.

The refractive index, $n$ , can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is $v = c/ n$ , and similarly the wavelength in that medium is $λ = λ 0 / n$ , where $λ 0$ is the wavelength of that light in vacuum. This implies that vacuum has a refractive index of 1, and assumes that the frequency ( $f = v / λ$ ) of the wave is not affected by the refractive index.

View the full Wikipedia page for Refractive index

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Speed of light in vacuum in the context of Invariant (physics)

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⭐ Core Definition: Speed of light in vacuum

Speed of light in vacuum in the context of Refractive index