What Is Light Dispersion?

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Light dispersion is the way white light is split up into different colors when entering a different medium. Find out how a prism can show the splitting of white light into a rainbow with help from a science teacher in this free video on physical science.

Part of the Video Series: Physical & Life Science
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Video Transcript

Hi, I'm Steve Jones and I'm going to explain what light dispersion is. Now light dispersion is something that's been seen for a long time but to explain it was not so easy. But now we think of light as a wave motion, it's much easier. Light is a wave motion and contains many different wavelengths which represent the different colors. There are not just three colors, there are millions and millions and millions of colors, colors through a whole spectrum, that's why we call it a light spectrum going from red through to blue. Now dispersion is the way light is split up into the different colors and it is split up into the different colors when it enters a different medium. And if we're in air here and if this is say glass, then light when it travels from air to glass will change it's speed. In fact the speed of light changes to about two thirds of what it was in air. So as it enters the glass, it changes speed and the different colors of light slow down by different amounts. So this difference in the slowing down of the light causes it to split up into different colors because the different colors bend therefore by different amounts. And it is this that we we see when we produce a spectrum. So white light entering a prism splits up within the prism into the different colors and as it comes out again it's bent yet again splitting further into what we call the colors of the rainbow. When we see a rainbow, this is an example of dispersion because the light is entering a raindrop and a raindrop is just like the glass here, it's water, slightly lower refractive index, it doesn't bend it quite so much, it doesn't slow the light down quite as much, doesn't bend quite as much and therefore we still get the spectrum but not quite as separated. But here we are, this is what light dispersion is, light dispersion is the separating of white light into the different colors which it already contains because it contains many different wavelengths of light.

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