![]() ![]() On a road, the tires can get good traction. So this is the passenger compartment, and it has four wheels on the car. But when you think about refraction I actually like to think of it as kind of a, as a bit of a vehicle, and to imagine that, let's imagine that I had a car. Sometimes you want to treat it as a ray, sometimes you want to treat it as a wave, sometimes you want to treat it as a photon. But just to-before I go into the math of actually how to figure out these angles relative to the velocities of light in the different media I want to give you an intuitive understanding of not why it bends, 'cause I'm not telling you actually how light works this is really more of an observed property and light, as we'll learn, as we do more and more videos about it, can get pretty confusing. And before I give you the actual equation of how these two things relate and how they're related to the speed of light in these two media- and just remember, once again, you're never going to have vacuum against water, the water would evaporate because there's no pressure on it and all of that type of thing. This is the incident angle, or angle of incidence, and this is the refraction angle. And this angle right here, theta 2, is the refraction. It's going to go down, in that direction just like that. Instead of continuing to go in that same direction, it's going to bend a little bit. What you're going to have is is this ray is actually going to switch direction, it's actually going to bend. But for the sake of argument, let's just say that this is a medium where light will travel slower. Normally, the water, since there's no pressure, it would evaporate and all the rest. This isn't something you would normally just see in nature but let's just think about it a little bit. So what will happen, and actually, that's kind of an unrealistic- well, just for the sake of argument, let's say we have water going right up against a vacuum. And let's say that this medium down here, I don't know, let's say it's water. There's nothing there, no air, no water, no nothing, that's where the light travels the fastest. And let's say we have the incident light ray coming in at some, at some angle theta 1, just like that.what will happen-and so let's say that this up here, this is a vacuum. So let's say-so that's the perpendicular right there, actually let me continue the perpendicular all the way down like that. Refraction, you still have the light coming in to the interface between the two surfaces. So in this situation, we will be dealing with refraction. ![]() What we want to cover in this video is when the light actually doesn't just bounce off of a surface but starts going through a different medium. That's essentially what we learned the last couple of videos. So that angle right there is going to be the same as that angle right there. We saw that before, and those angles are measured relative to a perpendicular. And if the surface is smooth, the incident angle is going to be the same thing as the reflected angle. And that's just the idea of the light rays bouncing off of a surface. In the last couple of videos we talked about reflection. This also explains how the beam of light DOESN'T BEND when you shine the beam along the normal the two sets of photons hit the surface at exactly the same time, so the light doesn't bend it just becomes slower. If the beam didn't bend, the beam wouldn't even be a beam, as the two lines of photons wouldn't be in the same line. Since the photons in the beginning of the other side of the beam don't hit the surface at the same time, there's a kind of a lag, and the beam bends. When you shine the beam of light on the surface that separates the two media, the photons in the beginning of one side of the beam hit the surface first, right? So they're the first set of photons to become slower (entering denser medium). The photons keep bumping into all sorts of particles in the medium. It doesn't have that much space to travel freely. The beam of light is slower in a denser medium because it's movement is hindered by lots of particles (in the media), compared to a rarer medium. Alright, let's take a beam of light, travelling from an optically rarer medium to an optically denser medium, say air and glass respectively. ![]()
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