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Case 3: An Object Closer to the Lens Than F1:
Here is the lens diagram, with the object already in place, and the first ray drawn:  This time something strange is going to happen. If you think ahead to the next step, you can see that the second ray, that must go through F1, will not hit the lens at all, much less intersect with our first ray here! What we're going to do is extend the first ray backwards as if it had come directly from F2, like this:  Now draw the second ray, the one that is supposed to leave from the top of the object. But instead, imagine a ray that has come from F1, and passes through the object's top point. This ray will go on to hit the lens, and refract through parallel to the base line, as before:  Now you should see the problem. The rays emerging on the right side of the lens don't intersect at all ... they diverge! But there's one more step. Take that last ray, (the green one) at the point it hit the lens, and extend it backwards and parallel to the base line. Like this:  Now the 'extensions of the rays backwards' do actually intersect, but on the same side of the lens as the object. The image shown here, located where they cross, is right-side up, and bigger than the original object. But wait, there's more! This is a virtual image. You can see it, but it can't be projected onto a piece of paper like before. Imagine you're holding a magnifying glass and looking at a penny that's below it, and within the focal distance. You will see an upright, enlarged penny, and it will appear as if it's below the magnifying glass too! This is a virtual image, and it's how a magnifying glass works! right-side up and larger than the object, and it's a virtual image. 'Virtual' means it really doesn't exist, in the sense that it can't be projected onto anything. The image of yourself in a mirror, for example, is also virtual; there isn't really a back side to a mirror with your image in it ... unless, of course, your name is Alice ... |