# Physical significance of Refractive index

1. Dec 10, 2012

### mikeanndy

What is the physical significance of Refractive Index(RI) ?

2. Dec 10, 2012

### Drakkith

Staff Emeritus
Can you be more specific in your question? What exactly are you wanting to know?

3. Dec 10, 2012

### davenn

well for work I have done in petrology ( study of minerals) refractive index is very significant because dofferent minerals can be identified by they refractive indicies

just one example :)

Dave

4. Dec 10, 2012

### ThereIam

The refractive index relates how quickly light travels through a given medium. It's a the number by which you divide the speed of light in a vacuum to get the speed of light in the given medium. Or, the number by which you divide the wavelength of the light in a vacuum to get the wavelength of the light the given medium.

I'd recommend looking at the Wikipedia article:

http://en.wikipedia.org/wiki/Refractive_index

5. Dec 11, 2012

### Philip Wood

So when the light changes medium it changes speed. If the light beam approaches the interface between media obliquely, this change of speed gives rise to refraction: a change in the direction of travel of the beam. A very simple formula (see wikipedia article on refraction) links angles of the beam to the normal in the two media to the ratio of refractive indices of the media.

6. Dec 11, 2012

### Andy Resnick

The refractive index is used in the continuum model of matter and parametrizes how matter interacts with electromagnetic radiation. The refractive index is used to describe reflection, refraction, dispersion, absorption, birefringence, and various nonlinear effects (Kerr, harmonic generation, self-phase modulation, etc.).

The refractive index can be 'split' into the permittivity and permeability, referring to how the material responds to either an electric or magnetic field, and can then be used to model additional material properties.

7. Dec 12, 2012

### sophiecentaur

Refractive index is actually a complex quantity and it includes a loss component which may be significant in some materials.

8. Dec 12, 2012

### DeShark

Refractive index is not only complex, but depends on the frequency of the light for a given material. Generally, though, it's stated for yellow light (more precisely the doublet sodium D-line).

The fact that the refractive index depends on the frequency of light accounts for things such as the greenhouse effect, whereby a material (such as glass) can absorb certain wavelengths, but allows other wavelengths to pass through. It also accounts for a prism splitting the light up into it's different colours.

9. Dec 13, 2012

### andrien

one can derive an expression for refractive index in classical electrodynamics if one assumes that electron is bounded to atom by a restoring force.

10. Dec 13, 2012

### sophiecentaur

The Appleton Hartree equation derives the complex refractive index for EM waves in a plasma. Useful for predictions of Ionospheric Propagation using ray tracing methods, for example. It gives speed and loss in the medium.