Why does dispersion occur physics

In the Light and Color unit of The Physics Classroom Tutorial, the visible light spectrum was introduced and discussed. Visible light, also known as white light, consists of a collection of component colors.

These colors are often observed as light passes through a triangular prism. Upon passage through the prism, the white light is separated into its component colors - red, orange, yellow, green, blue and violet.

The separation of visible light into its different colors is known as dispersion. It was mentioned in the Light and Color unit that each color is characteristic of a distinct wave frequency; and different frequencies of light waves will bend varying amounts upon passage through a prism.

In this unit, we will investigate the dispersion of light in more detail, pondering the reasons why different frequencies of light bend or refract different amounts when passing through the prism. Earlier in this unit, the concept of optical density was introduced. Different materials are distinguished from each other by their different optical densities. The optical density is simply a measure of the tendency of a material to slow down light as it travels through it.

As mentioned earlier, a light wave traveling through a transparent material interacts with the atoms of that material. When a light wave impinges upon an atom of the material, it is absorbed by that atom. The absorbed energy causes the electrons in the atom to vibrate. If the frequency of the light wave does not match the resonance frequency of the vibrating electrons, then the light will be reemitted by the atom at the same frequency at which it impinged upon it.

The light wave then travels through the interatomic vacuum towards the next atom of the material. Once it impinges upon the next atom, the process of absorption and re-emission is repeated.

The optical density of a material is the result of the tendency of the atoms of a material to maintain the absorbed energy of the light wave in the form of vibrating electrons before reemitting it as a new electromagnetic disturbance.

Thus, while a light wave travels through a vacuum at a speed of c 3. The index of refraction value n provides a quantitative expression of the optical density of a given medium. Next lesson. Current timeTotal duration Google Classroom Facebook Twitter. Video transcript Voiceover: Check out this ray of light. When it enters a new medium, like water, its path will bend, and the larger the index of refraction of the new medium, the more the light will bend from its initial direction that it had in the air.

This follows from Snell's Law, since if the index of refraction is larger, the angle of the refracted light must be smaller, and in order to have a smaller angle from the normal line, the light ray has to bend more from its initial direction.

But here's the interesting thing, when you send in white light, composed of all visible wave lengths, the colors will disperse and get separated from each other.

We call this separation of light, dispersion. Science eStore. Question Why does dispersion take place when light is passed through prism and not through glass slab? Asked by: Kavita Answer A light ray is refracted bent when it passes from one medium to another at an angle and its speed changes. At the interface, it is bent in one direction if the material it enters is denser when light slows down and in the OTHER direction if the material is less dense when light speeds up.

Because different wavelengths colors of light travel through a medium at different speeds, the amount of bending is different for different wavelengths. Violet is bent the most and red the least because violet light has a shorter wavelength, and short wavelengths travel more slowly through a medium than longer ones do. Because white light is made up of ALL visible wavelengths, its colors can be separated dispersed by this difference in behavior.

When light passes through glass, it encounters TWO interfaces--one entering and the other leaving. It slows down at the first interface and speeds back up at the second.

If the two interface surfaces are parallel to each other, as in a 'slab' of glass, all of the bending and dispersion that takes place at the first interfaces is exactly reversed at the second, 'undoing' the effect of the first interface; so although the emerging ray of light is displaced slightly from the entering ray, it travels in the same direction as the incoming ray and all wavelengths that separated at the first interface are re-combined. If the second interface is NOT parallel to the first, as in a prism, the effects of the first interface are NOT reversed and the colors separated at that interface continue along different paths upon leaving the glass.

Answered by: Paul Walorski, B.