Refraction and frequency | Waves | Middle school physics | Khan Academy
When light is going through a uniform medium like the air, or as we know, light can go through vacuum, so nothing at all, we imagine it going in a straight line. But we see something really interesting happening here when it hits this glass prism. I know it just looks like a gray triangle to you, but imagine it as a triangular piece of glass, and it's hitting it at an angle.
What this animation shows us is that the path of the light actually gets bent. Not only does it get bent, but the different frequencies of the light get bent by different amounts. Now, if you were to look at this with your eyes, you wouldn't be able to see the actual waves like we're seeing in this diagram right over here. You would just see how your brain, or how your mind, perceives the various frequencies.
That's why they made the higher frequencies here more like a violet or a purple color, and that's why they made the lower frequencies here more of a red color, because that's how your brain, or your mind, would perceive them. But you can see as this light goes from, let's say, the vacuum to this prism to this crystal or this glass, the high frequency light gets bent more. The low frequency light, which still gets bent, gets bent less, and then that essentially spreads out all the wavelengths.
When we have white light, it has all of the visible wavelengths in it. But when it hits a prism like this, if you imagine a triangular piece of glass or crystal and it hits it at an angle, well then the different wavelengths spread out. If you were to put a piece of paper here, you would see a rainbow, and that's actually how rainbows are formed.
A bunch of water particles in the air refract light exactly like this. This process of when light goes from one transparent medium to another, or a vacuum to some other medium that it can travel through that's transparent, if it hits it at an angle, it can get bent, which is what we call refraction. This is why when you look at a cup of water or at a pool at an angle, you're not seeing directly through the pool; the image gets distorted.