# Help Zone

### Student Question

Secondary V • 2yr.

How is the phenomenon of dispersion explained?

Physics

## Explanations (1)

• Explanation from Alloprof

Explanation from Alloprof

This Explanation was submitted by a member of the Alloprof team.

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Team Alloprof • 2yr.

Dispersion takes place when white light is separated into all of its constituent colors.

Indeed, white light is the union of the colors of the rainbow!

This phenomenon is observed each time a ray of white light changes medium and is refracted. However, it is often imperceptible, especially when the rays are not refracted much.

The explanation for this phenomenon is as follows: as each color of light does not have the same energy, its speed in each medium is not the same. As the index of refraction (IOR; which calculates the angle by which an incident ray of light will be refracted) is expressed as a function of the speed of the rays of light in a certain medium, the IOR for each color is not the same:

$$n = c \bullet v$$

Legend:

• n: index of refraction of a given medium

• c: speed of light in vacuum (= 300,000 m / s)

• v: speed of light in a given medium

So each ray of monochromatic light (of a single color) is not equally refracted. Thus, some colors are more deviated than others, causing dispersion.

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