Lenses and Light
When light passes through a curved transparent substance, it is refracted. A curved transparent substance is called a lens. There are other things besides glasses that have lenses e.g. cameras,binoculars and microscopes.
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There are two basic types of lenses: convex or concave. Convex lenses bulge out toward you, and are thicker in the middle than at the edges. Convex lenses cause light waves to come together (converge) as they bend towards the thicker part of the lens. The convergence causes the light rays to be focused to a sharp point of light. This type of lens magnifies things. Convex lenses help people who are farsighted.
Convex Lens: Light rays converge.
Concave Lens: Light rays diverge.
Concave lenses are sunken in the middle. They are thinner in the middle and thicker at the edges. This curve causes the light rays to be spread apart, which makes images look smaller and farther away. People who are nearsighted benefit from concave lenses.
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Farsighted people have difficulty seeing objects which are far away because the light from the object is focused behind the retina. |
A convex lens corrects farsightedness problems. |
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Nearsighted people have difficulty seeing objects which are far away because the light from the object is focuses in front of the retina. |
A concave lens corrects nearsighted problems. |
