Correcting imperfect visionClick HERE to go to an interactive where you can correct poor vision with different lenses. NOTE: This requires Adobe Flash, which may not work on your computer.
Question
1. After doing the "Refraction with Lenses" experiments, see if you can explain how a convex lens can correct the vision of a far sighted person.
|
|
If you watch the video on the left, it will help you answer the question on your "Refraction Through Lenses" worksheet.
|
Why goggles allow you to see well under water
One of my students asked how goggles help you see more clearly underwater. I didn't explain it very well, so here is a better explanation with an image.
When you look at things underwater, they appear blurry. What I haven't shared with you is that you actually have 2 lenses in your eyes - the liquid-filled cornea and the lens. The lens, as I mentioned earlier, allows you to focus light on your retina when your muscles pull it flat (thin biconvex lens) or relax to make it fatter (thick biconvex lens). But before the light reaches your lens, it must pass through the cornea first. Because the light passes from less optically dense air into the more optically dense liquid cornea, it slows down and bends towards normal. When it then enters your lens, it slows down again. This is like putting 2 biconvex lenses together (as we did in our "Refraction through Lenses" experiment. Remember that this caused the focal distance to shorten? |
Because water is nearly the same optical density as your cornea (1.33 v. 1.38) , the light passing from the water through your cornea does not bend nearly as much as if it was passing from air through your cornea, which effectively eliminates the 1st bending of light by the cornea before it goes through our lens. This is like taking away the first biconcave lens in our experiment - it lengthens the focal distance. Since our eye muscles can only relax so much, our lens can only get so thick, which means that light can only bend so much. Therefore, we cannot bend the light enough to focus the light on our retina. The focal point is effectively behind your retina - much like if you were far sighted. This gives us the fuzzy images when we open our eyes underwater.
Adding glass goggles helps restore our vision by placing air back into the equation. The glass of the goggles also refracts the image slightly and makes the images appear larger - much like a magnifying lens.
Adding glass goggles helps restore our vision by placing air back into the equation. The glass of the goggles also refracts the image slightly and makes the images appear larger - much like a magnifying lens.