# A report onLight, Speed of light and Refractive index                                          In optics, the refractive index ( refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.

- Refractive index

All forms of electromagnetic radiation, including visible light, travel at the speed of light.

- Speed of light

Its speed in a vacuum, 299 792 458 metres a second (m/s), is one of the fundamental constants of nature.

- Light

The speed at which light propagates through transparent materials, such as glass or air, is less than c; similarly, the speed of electromagnetic waves in wire cables is slower than c. The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material (

- Speed of light

where θ1 is the angle between the ray and the surface normal in the first medium, θ2 is the angle between the ray and the surface normal in the second medium and n1 and n2 are the indices of refraction, n = 1 in a vacuum and n > 1 in a transparent substance.

- Light

If the electrons emit a light wave which is 270° out of phase with the light wave shaking them, it will cause the wave to travel faster. This is called "anomalous refraction", and is observed close to absorption lines (typically in infrared spectra), with X-rays in ordinary materials, and with radio waves in Earth's ionosphere. It corresponds to a permittivity less than 1, which causes the refractive index to be also less than unity and the phase velocity of light greater than the speed of light in vacuum c (note that the signal velocity is still less than c, as discussed above). If the response is sufficiently strong and out-of-phase, the result is a negative value of permittivity and imaginary index of refraction, as observed in metals or plasma.

- Refractive index ## 1 related topic with Alpha ## Polarization (waves)

Property applying to transverse waves that specifies the geometrical orientation of the oscillations.

Property applying to transverse waves that specifies the geometrical orientation of the oscillations.                      Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, and transverse sound waves (shear waves) in solids.

Even in isotropic media, so-called inhomogeneous waves can be launched into a medium whose refractive index has a significant imaginary part (or "extinction coefficient") such as metals; these fields are also not strictly transverse.

In a vacuum, the components of the electric field propagate at the speed of light, so that the phase of the wave varies in space and time while the polarization state does not.