Density and refractive index relationship advice

How is density related to refractive index? | Naked Science Forum

How does density affect the refractive index of a liquid? For any particular material the relation between density and refractive index is very. So in general, they would not follow the relation you want. Silicon might be This is a graph of the refractive index and density. As you can see. So indeed our density does effect our index of refraction. arrives at the same relationship between molecular density and refraction index as I.

The light wave traveling in the medium is the macroscopic superposition sum of all such contributions in the material: This wave is typically a wave with the same frequency but shorter wavelength than the original, leading to a slowing of the wave's phase velocity.

Most of the radiation from oscillating material charges will modify the incoming wave, changing its velocity. However, some net energy will be radiated in other directions or even at other frequencies see scattering.

Depending on the relative phase of the original driving wave and the waves radiated by the charge motion, there are several possibilities: This is the normal refraction of transparent materials like glass or water, and corresponds to a refractive index which is real and greater than 1. This is called "anomalous refraction", and is observed close to absorption lines typically in infrared spectrawith 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.

This is light absorption in opaque materials and corresponds to an imaginary refractive index. If the electrons emit a light wave which is in phase with the light wave shaking them, it will amplify the light wave. This is rare, but occurs in lasers due to stimulated emission. It corresponds to an imaginary index of refraction, with the opposite sign to that of absorption. Dispersion[ edit ] Light of different colors has slightly different refractive indices in water and therefore shows up at different positions in the rainbow.

Optical Density and Light Speed

In a prism, dispersion causes different colors to refract at different angles, splitting white light into a rainbow of colors. The variation of refractive index with wavelength for various glasses. The shaded zone indicates the range of visible light. Dispersion optics The refractive index of materials varies with the wavelength and frequency of light.

Dispersion also causes the focal length of lenses to be wavelength dependent. This is a type of chromatic aberrationwhich often needs to be corrected for in imaging systems. The cycle of absorption and reemission continues as the energy is transported from particle to particle through the bulk of a medium.


Every photon bundle of electromagnetic energy travels between the interatomic void at a speed of c; yet time delay involved in the process of being absorbed and reemitted by the atoms of the material lowers the net speed of transport from one end of the medium to the other. Optical Density and the Index of Refraction Like any wave, the speed of a light wave is dependent upon the properties of the medium. In the case of an electromagnetic wave, the speed of the wave depends upon the optical density of that material.

The optical density of a medium is not the same as its physical density. The optical density of a material relates to the sluggish tendency of the atoms of a material to maintain the absorbed energy of an electromagnetic wave in the form of vibrating electrons before reemitting it as a new electromagnetic disturbance. The more optically dense that a material is, the slower that a wave will move through the material.

One indicator of the optical density of a material is the index of refraction value of the material. Index of refraction values represented by the symbol n are numerical index values that are expressed relative to the speed of light in a vacuum. The index of refraction value of a material is a number that indicates the number of times slower that a light wave would be in that material than it is in a vacuum.

A vacuum is given an n value of 1.

Optical Density and Light Speed

The n values of other materials are found from the following equation: The table below lists index of refraction values for a variety of medium. The materials listed at the top of the table are those through which light travels fastest; these are the least optically dense materials. The materials listed at the bottom of the table are those through which light travels slowest; these are the most optically dense materials.

So as the index of refraction value increases, the optical density increases, and the speed of light in that material decreases.