Ray Diagrams for Converging Lenses

by Patrick Ford
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Hey, guys. Now what? We're gonna talk about our ray diagrams for converging lenses. Okay, We talked about Ray diagrams for converging mirrors, but a mirrors job is to reflect light and produce an image in front of it. Ah, lenses job is to transmit light and produce an image behind it. So we're gonna see how that works now, conceptually with ray diagrams. All right, let's get to it. When light strikes the surface of a mirror, it reflects, right? This is already something we talked about a bunch. But when light strikes the surface of a lens, it transmits lenses. You're gonna be made out of transparent material that allows the passage of light through it. The transmitted light undergoes refraction, just like the reflected light off of a mirror obeys the law of reflection. Okay, converging lenses, right. As the name implies, our lenses that allow the convergence of light when you have initially column ated light like you do here. When it passes through the lens, those light rays all bend towards the central axis and therefore they converge on a points. This is a point of convergence. The point on the opposite side of the lens where the light converges is known as what guys? We know it as the focus, same as we had four mirrors. The thing about lenses, though, is that in order to draw diagrams properly, we have to represent focuses on both sides of the lens. So whatever this focal length is, F we're going toe. Have a second focus that same distance f on the front side of the lens as well. It's just a tool that we need to use in order to draw diagrams properly. Okay, the most common type of converging lens and the one shown in the figure above is called a by convex lens. It's by convex because both sides are convex surfaces. Okay, and it looks convex. Either way, you look at it. You could rotate this mirror. I'm sorry, this lens and it's gonna look convex, no matter how you look at it. Okay, Just like with mirrors, we can draw rate diagrams to find information. Qualitative information about the image is formed by lenses, but we need an associate ID set of rules for lenses, just like we had a set of rules for mirrors. Okay, so those rules are gonna be presented here to draw diagrams for converging lenses. You need to draw two of the following lines, just like the same thing for mirrors, a line parallel to the central axis, then through the lens towards the far focus. By that, I mean the focus on the other side of the lens. Second, aligned through the near focus the focus on the side of the lens of the object, then through the lens parallel to central access. Okay and, lastly, aligned to the very center of the lens that passes through undefended, that line will not get refracted. It's gonna pass through with the exact same angle. Let's do an example to illustrate this process. Draw the image location for the following converging limbs. Is the image upright or inverted? And in order to draw diagrams, you need some sort of ruler or some sort of straight edged object. What I have is my trusty protractor, because that's what I'm using. Instead of a ruler. Now we're going to draw two of the lines and find where they intersect. We could draw the third line, and it would intersect where the other to do as well all we need to know where the image is located is to find a point where two lines intersect. So the first line I'm going to draw is parallel to the central axis and ferree diagrams. You always draw them to the center of the lens. Thes types of lenses that we're gonna be dealing with are called thin lenses. Which means that compared to the radius of curvature of the lens, they are very, very thin. Okay, so they're essentially occupying a central line. Okay, so you're always going to that center line that I have indicated then from the center line, through the focus. Okay, The next line is going to be from the object through the focus to the center line of the lens and then parallel to the central axis of our lens. And look, you there, I just barely caught it. So here is the point of convergence. Because this blue ray have blue Ray is just going to continue and right there is clearly the point of convergence. Now, is this image upright or inverted? We're going to use the same convention that we used for mirrors. If the conversion of light is below the horror of the central axis, the horizontal axis. Then it's inverted. If it's above the central axis, then it's upright. This is clearly below the central axis, so this image is inverted, all right. And that wraps up our talk on ray diagrams for converging lenses. Thanks for watching guys.