Bending Light with RefractionLenses are pieces of glass that bend light. The easiest thing to think about is lenses in eyeglasses. People who do not have 20/20 vision might see things a little out of focus. They wear glasses or contact lenses to make their sight clearer. Those glasses have specially ground lenses that bend the rays of light just enough to focus the image for the person to see properly. All lenses bend and refract rays of light.
In the refraction section we said that light changes speeds when it moves from one medium to another. A medium is a substance like water, air, or glass. When light slows down or speeds up it changes direction a little bit. There are three basic shapes that a lens can have: concave, convex, and planar. A concave shape is bowed inward, like looking into a mixing bowl. Convex is just the opposite, bowed outward. Have you ever seen those mirrors in the grocery stores, where everything is reflected in a spherical way? That's convex. Planar is just that, a plane. It's a flat surface. Just think of a planar mirror on your wall.
Using LensesTelescopes and microscopes are excellent examples of how lenses are used every day. By using different combinations of lenses, light is focused to create an image we could not see with the naked eye. Telescopes are able to see very distant objects that are very small to our sight and magnify them so we can see the details. The larger telescopes offer a greater ability to see objects that are more distant. Microscopes work with a similar idea but are concerned with size, not distance. Microscopes enlarge very small objects that are close to the viewer.
Using PrismsPrisms are a very special type of lens. When refraction is at work in a prism it breaks the beam of visible light into its basic colors. In visible light, the magic colors you can see are red, orange, yellow, green, blue, indigo, and violet. Scientists say ROY-G-BIV. A prism is made up of two planar surfaces at an angle. It uses the slower speed of light in glass to its advantage by refracting the light twice. Because of the different wavelengths of light, each color is refracted a different amount. When the light ray leaves the prism, it speeds up again (entering the air) and refracts a second time. That second dispersal creates the colorful spectrum of colors.
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Concave and Convex Water Lenses (NASA Video)
Useful Reference MaterialsEncyclopedia.com (Refractive Index):