Everyone. Welcome back. So in this video, we're gonna start talking about another phenomenon of lights uh called refraction. Now, we're actually not going to talk about the specifics of refraction. In this video, we're gonna talk about an important variable that you'll need for that video called the index of refraction and we'll get to it soon. All right. So let's just get started. Now, remember when we talk about light, we use this variable C which stands for the speed of light in a vacuum. This is the three times 10 of the 8 m per second. The problem is in everyday life, light travels in all different kinds of materials like air and water and glass, things like that. So what you need to know here is that in all other materials, light always travels slower. It's kind of like how we talked about the speed of sound, the speed of sound differed depending on the material. So does light and light always travels slower than anything that's not a vacuum. All right. So that actually kind of brings us to this important variable called the index of refraction. It's given by the variables N over here. And basically what it is is it's a ratio, it's a ratio of C. So C is the numerator to the speed of light in that material. So in other words, it's a ratio of the speed of light in a vacuum to the speed of light in a particular material. And that's what N is. So you can actually kind of expand this a little bit and rewrite this as just basically just three times 10 of the 8 m per second divided by whatever that speed in that material is. So there's really only two variables in this equation N and V because C is a constant. All right. Now, actually, I'm gonna get back to this point in just a second because we can just jump right into our example. I'm gonna show you how this works. So we uh we're told here that when light enters water, it slows to a speed of approximately 2.25 times 10 of the 8 m per second. And we're gonna calculate the index of refraction for water. All right. So you'll see these tables uh very commonly in your textbooks. They'll have all different kinds of, of uh variables. You'll never have to memorize them, they'll always be given to you. So don't worry about that. All right. So we're told the speed of light in water, which variable is that, is that N, is that C, is that V? Well, hopefully, you guys realize that the C is always just gonna be a constant and N is the index of a fraction. So really, they're actually just telling you, V there's telling you the speed of light in that material. So how do we calculate NN is just equal to C over V? So in other words, it's just equal to three times 10 to the eighth, divided by two points 25 times 10 to the eighth. Now, here's just a really quick shortcut. When you plug this into your calculator, if these have the same base of 10, you can kind of just ignore them and you can only just do, uh you could just do three divided by 2.25. Anyway, what you should get here is you should get 1.33. And if you look in your textbook, that is exactly what the index of a fraction of light is. All right. It's 1.33. Now notice that we got a number that was greater than one and that actually kind of brings me back to my point over here because what we said here is that light always travels slower in any material. So in other words, if V is always less, then C and what we can see from this equation here is that if you always have a lo a number that's lower than C in the denominator, then that means you're always gonna end up with a number that is lower or greater than one, less than, or greater. It's actually gonna be greater. So it's gonna be greater than one and notice how all of these numbers over here are gonna be greater than one. That will always be the case. You'll never see something that's less than one. All right. So that's just what you need to know about the index of refraction. The very last point that I have to make here actually has to do with air because it's a very common material that you'll see in problems. So if you look at this table here, it says that the index of refraction is very close to one, it's 1.0003. So usually what happens is that in most problems, you can kind of just approximate it and use one for the index of refraction when you're talking about air. All right, that's it for this folks. Let me know if you have any questions and I'll see you in the next video.