# How and why does a prism split white light into the colour spectrum

[Solved] How and why does a prism split white light into the colour spectrum

## Homework Statement

How and why does a prism split white light into the colour spectrum?

## Homework Equations

Red light has a lower frequency than violet light. As speed of light = wavelength * frequency, red light has a larger wavelength than violet light.

## The Attempt at a Solution

For a prism to split the visible waves of varying wavelengths that collectively add up to form white light, the angles at which the waves are bent need to be different between the two extremes of red light and violet light.

Where I'm stuck is, how and why is the angle of refraction different between red light waves and violet light waves?

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Borek
Mentor
Light speed in the glass is a function of the wavelength.

So, slower light is refracted more then faster light? How do you relate light speed and wavelength?

Edit: Solved, found it: http://en.wikipedia.org/wiki/Sellmeier_equation
Keep in mind that this is purely an empirical relationship, i.e., you can measure a material's refractive index at various wavelengths and then find a set of "B"s and "C"s so that Sellmeier's equation makes a generally good fit. However, note that it predicts an infinite refractive index whenever the wavelength is equal to one of the "C"s. Check out "anomalous dispersion" for more info.

Borek
Mentor
So, slower light is refracted more then faster light?
Yes. Do you know how refractive index depends on the speed?

How do you relate light speed and wavelength?
Simplest answer: you find it experimentally.

Yes. Do you know how refractive index depends on the speed?
Snell's Law, n1/n2 = v1/v2, conveniently also = sin(o1)/sin(o2)

Borek
Mentor
So - for introductory physics - you know everything you need Good, thanks. 