How do lens magnify objects?

Answer 1

Quick Answer: by refracting light at differring but predictable rates through a transparent or translucent material. Lots of information can be found here: http://en.wikipedia.org/wiki/Lens_(optics) http://en.wikipedia.org/wiki/Speed_of_light http://en.wikipedia.org/wiki/Magnifying_glass Here is my longer but (I think) more pleasant thought experiment intended for non-scientific types: Light does not travel instantly, but it is still as fast as you can get. In a complete vacuum (meaning empty space with absolutely no particles for the light to interact with) light travels at the universally constant speed of 299,792,458 meters per second, or to put it scientifically: very very fast. This speed is absolutely unchanging as long as the light does not interact with any matter, such as water, air, or the glass or plastic of an optical lens. Since light is very difficult to imagine on its own, think of a particle of light like a car that can only go 50 miles an hour and it doesn't have a steering wheel so it only drives straight forward. It can't go slower, it can't go faster, it can't go left, it can't go right. Just 50 miles an hour straight ahead. It's just the way they are made at the factory. Lets call this car a Photon. Now imagine a thousand of these Photon cars lined up in a field. The field is completely empty and the cars can go anywhere they want. There are no traffic signs, no potholes, no houses, nothing. The cars can drive all over the field and never hit a thing. Now lets get these cars to race each other. Imagine we line up the thousand Photon cars at the edge of the field. The race starts and it is really boring. The cars all go 50 miles an hour and they all get to the other edge of the field at the same time. This is what light is like in a vacuum or outer space. Nothing to get in its way. OK, that was a boring race so lets do some construction to try and spice things up. Across the whole field we put down a big old 6 inch high speedbump. It's a mile wide and straight as an arrow. The race starts and all the cars hit the speedbump at 50 miles an hour. All the Photon cars are going the same speed and so they hit the speedbump at the same time. All the cars get over the speedbump simultaneously and they all finish the race at the same time, again. So boring! This is what it is like for light to hit a flat pane of glass. The glass is the same thickness throughout and the light particles are all going the same speed, so they hit the glass and pass through it all at the same rate. It's a boring race so the light looks exactly the same on one side as the other ... just a little bit later since it went over a little speedbump. So now lets line up the Photon cars at the edge of the field and get ready for another race. This time, lets really make it interesting. We call up a construction company and have them dig a humongous, bowl-shaped hole in the field. They make a nice circular crater right where the speedbump used to be. They dig out enough dirt so the big round hole is a mile around in a big circle a thousand feet deep. We start the race again. All our little Photons start at 50 miles an hour, just like before, all in a long line. The cars are all going at the same speed and the cars in the very middle of the row are the first to get to the rim of the crater. The cars on the left and right sides are still on flat land and they still have a while to drive before they hit the edge of the circular hole. As the line of cars races across what used to be a flat field, they slowly dip out of our view as they dive down into the great hole in the ground. Imagine the car in the very middle of the row; that poor car has to drive the furthest distance! He is travelling right through the very middle, which also happens to be the deepest part of the big bowl. He got in the crater first and he'll be the last to drive out. Now imagine the two cars on the farthest left and right of the row of cars. They have it easy as they drive across completely flat field until they hit the tip top of the left and right side of the big bowl. When those left and right cars hit the rim of the crater though, it turns them since the edge of the bowl is practically a straight wall of dirt. The cars on the left get turned right and the cars on the right get turned left. The cars in the middle don't really get turned since they hit the edge of the crater with their front two wheels, so for them, it is kind of just like going over the speedbump. For the right and left sides though, driving into that crater flips their side tires and they end up getting turned towards the middle and towards the other cars. So all the cars end up on a collision course with all the other cars! (Don't worry, no one gets hurt.) When the cars get to the finish line, the Photons on the right and left flanks finish first BUT, they are the most off course and have been turned the most. If the Photon cars in the middle of the row weren't still driving through the crater, they would cross paths. If we were to let the race go on past the finish line, all the cars would cross paths ... the leftmost cars would end up on the right side and the rightmost cars would end up on the left side. This is what happens in a convex lens: the outermost photons are bent to the middle while the middle photons barely bend at all. Their paths get closer and closer creating the effect of making small patches of light seem larger. If you hold a magnifying glass far enough away, you can see that the paths of photons will cross paths and switch sides, creating the effect that the image appears "upside down." This is certainly not a perfect analogy (about which I am sure there will be comments posted)and it is certainly a lot longer than I intended, but I had fun with this and hope you do as well :D Hopefully any editors will keep the spirit of the post at least :D Special thanks to wikipedia and to the magnifying glass I found in my kitchen.