# Wavelength sand refractive index

1. Sep 11, 2011

### Misr

why do refractive index vary with the wavelength?what makes the relation between wavelength and the refractive index reverse relation??and what makes the relation between frequency and wave length direct relation??does it has somethin to do with energy and the abiliy to penetrate bodies??Are there certain conditions for a prism to disperse light?should light fall at a certain angle on the prism?
Thanks

2. Sep 11, 2011

### Drakkith

Staff Emeritus
Different wavelengths affect the medium they are in differently. The result of this interaction determines the speed of the wave through the medium. See here for more: http://en.wikipedia.org/wiki/Refractive_index#Microscopic_explanation

Since light travels at the same velocity in a vacuum, the frequency and wavelength are always related. A 1 kilohertz radio signal photon oscillates 1,000 times per second. In a vacuum light travels at almost 300 million meters per second, so dividing the distance travelled by the number of times it oscillates (the frequency) will give you the wavelength, which is the distance between peaks in the oscillation. So a 1 kilohertz frequency photon has a wavelength of 299,792 meters, or about 300 kilometers. See here: http://science-edu.larc.nasa.gov/EDDOCS/wavelength.html

Yes, the further from perpindicular that the light enters the prism, the more it is dispersed. Past a certain angle I believe other effects start to happen, such as internal reflection, but I'm not sure on all the details.