Ray Diagrams for Diverging Lenses

by Patrick Ford
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Hey, guys, In this video, we're gonna talk about Ray diagrams for diverging lenses. We just took a look at Ray diagrams for converging lenses, so we know that these should be similar. But since the light diverges, we know ahead of time some things about the images that we're gonna be formed. All right, let's get to it. A diverging Linz will never focus light ever because when light rays pass through it, they spread further apart. They don't come closer together, so they will Onley produce virtual images. I have a picture here off initially column mated light passing through a diverging lens. And what it turns out toe happen is that if you were to look at the diverging light after it had passed through the lens, it all appears toe have come from a point. So we have an A parents convergence. This is almost identical to convex mirrors, except mirrors reflect light and lenses transmit light. Remember, just like with those convex mirrors, the light appears to focus on a point, which we call the apparent focus for good reason, though often times we'll just refer to it as a focus because physicist tend to be lazy now because light can pass through either side. We need to have a focus that exists on either side of the lens, just like we did for conversion lenses. Okay, This is also important in how we're going to draw our raid diagrams. Alright. The most common type of diverging lens is the one shown above, which is called a by con cave lens. It's by con cave because it's a con cave surface. Either way, you look at it. If you were to flip this lens, it would still look con cave Okay, just like with mirrors, weaken draw diagrams for these lenses to find out information about the images. We did it for converging lenses. Now we want to do it for diverging lenses and the rules. We're going to be very similar with slight differences. To draw diagrams for diverging lenses, you need to draw two of the following lines a line parallel to the central axis, then through the lens, away from the near focus. Okay, second, align towards the far focus, the focus on the other side of the lens, then through the lens and parallel to the central. Okay, axis. All right, And lastly, just like for converging lenses, a line through the center of the lens that passes through un deflected those. They're going to be our three. Raise that we're going to draw. We only need to draw two of them to find an intersection of light. But those were gonna be the three possible raise we can draw for ray diagrams of diverging lenses. Okay, let's do an example. Draw the image location for this. This should say diverging lens. Is the image upright or inverted? Okay, so before we even begin, is the image gonna be upright or inverted? What do you guys think? This is the diverging lens. So the Onley images that can produce our virtual images and virtual images air always upright. So before we do a single thing we know just through rationalization and our physics knowledge that this image is gonna have to be upright. I don't have to draw a single lot. If the question was is the image upright, you'd be done. But where is the image located for that? We do need to draw a diagram. So the first Ray is going to be from the object parallel to the central axis right to the center of the lens. That's where we always draw and then away from the near lens. Okay, so I'm drawing it on a line parallel to the near Linz, but away from it. And then I'm gonna trace the line back to the origin the apparent origin of that line. Because that's where your brain is gonna see that line coming from next. What I need to do is draw a line towards the far focus. Okay, but once it hits the center of the lens, then it becomes parallel to the central axis. Okay, And where does this line appear to come from? I need to trace it backwards. It appears to come from this direction, so you can see right there. There is an apparent convergence that is our virtual image. And because it's above the horizontal axis because it's above the central axis, we know that it's upright exactly as we had predicted. Alright, guys, that wraps up our discussion on ray diagrams for diverging lenses. Thanks for watching