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PhD., University of Maryland
Jonathan is a published author and recently completed a book on physics and applied mathematics.
Diffraction is the bending of a wave as it changes medium. Waves with small wavelengths, like light, show very little diffraction. Waves with large wavelengths like low pitched sound show major effects diffraction.
So let's talk about diffraction. Diffraction's a really simple concept but it's majorly confused by a lot of people. So let's try to get it right. Alright? Real real real simple.
A wave is a disturbance in a medium. that's what it is, okay? It disturbs the medium. So let's say that you've got a wave and there's some sort of boundary that it's trying to get around. Like you could imagine sound going through like a doorway or you could imagine a wave going through and there's a jetty, alright? So what happens after it goes past this boundary? Well, it's going to spread out to fill the medium, because it's a disturbance in the medium. So once the boundary's not there anymore, well jeez, it's going to spread out to fill the medium. That's called diffraction. So here's a wave coming in and then we've got a boundary. It's got to go through here. So it kind of chops off the wave here but then after the wave passes through the boundary it starts to spread out and fill in that part of the medium, alright? So that's diffraction.
Okay. Now, it's important to understand that the amount of diffraction that you'll see is of order the wavelength. So if you've got a really really really small wavelength, then you won't be able to observe the effects of diffraction. The best example of this is light. And this was actually used for centuries to argue that light is not a wave because it doesn't display diffraction. And you can see that very very very easily just by looking at shadows. Right? You've got light coming down where there's a boundary, oops, suddenly it's dark. Right? Now of course light really does display diffraction but the wavelength of light is so small that you have to look very very very carefully to see it. You can but you got to look really really really carefully. Alright.
Another example of something with a small wavelength is high pitched sound. You may not have noticed this but you may have. High pitched sound is easier to channel than low pitched sound. If you've got a really really really low bass, then it kind of causes everything to vibrate. You can't really channel it. But if you've got a very very very high pitched note, you can channel it out. Now of course if somebody's singing then that's going to go out in all directions anyway. She's not trying to channel it. But if it's sung through kind of like a tube, then it will be channeled of a lot more than large wavelength, low pitched sound.
Now, you've probably noticed this. If you're in a concert hall and you hear like the real real real low pitches, it really makes the whole concert hall vibrate. It's not at all directed at anything. So low pitched sound has major major major diffraction. Ocean waves also show major diffraction and in fact jetty's are used to channel ocean waves in a specific way using their diffractive property.
And that's diffraction.
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