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Anderson Video - Magnification

Professor Anderson
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 And so we can quantify the magnification. The magnification M is just related to the height of the image over the height of the object and that is directly related to how far away the image is versus how far away the object is. So in the last example when we had the object place right at C the image was also at C, but it was inverted. Negative 2 over 2 just means magnification of one but an inverted image. So if the magnification is less than zero, if it's a negative number, that just means the image is upside down. It's inverted. All right, let's talk about convex mirrors. Right now we just covered concave mirrors but of course you can have image formation with convex mirrors. Let's see how that works. Okay, so here's our convex mirror. And let's draw the center of it which is about there. And let's draw the focal position, which is about there. Notice the focus is over here on the right side of the mirror now, which means it's a negative number. So if I put my object right there how do I find the rays that are going to form the image? We do the same thing that we did before. We follow those three rules except we have to remember that the focus is over here and the center is right there. So this says that rays that are parallel parallel to the optic axis are going to go through the focus. But this thing is a mirror. Right, it's a convex mirror. So there's no real light ray that penetrates through the mirror, it becomes a dashed line. Okay, this was rule number one. All right. If it's a dashed line what that means is when you look at this mirror, it's going to look like it came from there. All right? What about rule number two? Rule number two was rays through the focus go parallel. All right. There's the focus. How do I get to it? I go like this. I get to the mirror, and it stops becoming a real ray, it in fact becomes a virtual ray. And this is ray two. I guess this one here is fine. Okay. That one looks good. Ray three is going to be the hard one to draw, okay? And before we do that, let's talk about Ray two. Ray two bounced off and went there. Okay so it looks like it came from there. And then ray three is the one that goes through the center. And if I go towards the center Off it goes, that's ray number three. And now this is a little hard to see but hopefully you can see that those three virtual rays all look like they are intercepting each other right there. Book might have a better picture of that. Sometimes it's a little hard to see up here on the screen exactly where it's intercepting but that should be about the right position. This is of course a virtual image. Because there's no real rays that are forming it. It is also demagnified. Because it's smaller than the object. And this is what they mean by the passenger-side mirror objects in the mirror are closer than they appear because it looks kind of small. Right? And there's that great scene in Jurassic Park where he's looking in the rearview mirror at T-rex and it says objects in the mirror may be bigger than they appear. Okay, and it is also upright as opposed to inverted. That's how you would describe it. This sort of mirror also obeys the mirror equation as long as you remember that stuff on the right side has a negative sign, stuff on the left side has a positive sign.