What are Convex and Concave Lenses?
Contributed by: Chapman F.
Date of creation 9/30/11

There are two types of lenses, convex and concave. Convex lenses curve outward so that when light passes through the lens it they light rays bend and spread apart which makes the view appear larger than it really is. Concave lenses curve inward so when the light rays pass through they come together and make the object smaller than it really is. When you look through a single sided lens backwards it works as the opposite type of lens.

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Figure 1: How convex and concave lenses with the eye.

Convex lenses are used and reading glasses so the user can see the items or be able to read better. Convex lenses make the item that is being focused on look bigger. Convex lenses are considered negative lenses because it has a steeper surface and a thinner center. Convex lenses are used in microscopes to make the items look bigger. Convex lenses are also used in cameras to zoom in the camera has layered convex lenses so when it zooms in the lens comes out and they separate making the image bigger.

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Figure 2: How light rays pass though convex lenses.


Concave lenses make the item appear smaller. One example is a peep-hole in a door. Someone Knocks on your door and you don’t know who it is, When you look through the peep-hole is shows you the whole area so you can see the whole person. Concave lenses are considered positive because they have steeper center and a thinner surface.

figure_2.jpg
Figure 3: How light rays pass though concave lenses.
Lenses
Lenses are pieces of glass, transparent plastic, or see- through metals that are curved on one or both sides. Lenses are classified be the amount that the two optical surfaces curve. Some types of lenses are in the picture below.
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Figure 4: Different types of lenses.


Eyes
The eyes have a part on them called the retina. The retina is a convex lens built into the eye. This helps us to see farther and more clearly. Photosensitive cells called rods and cones in the retina convert incident light energy into signals that optic nerves carry the signals to the brain.


GLOSSARY
Positive: In physics, the name given to one of the two types of electric charge. Protons are positively charged. Objects that are positively charged normally reach that state by losing electrons rather than by gaining protons.
Negative: In physics, the name given to one of the two types of electric charge. Protons are positively charged. Objects that are negatively charged have more electrons than protons.
Optical:constructed to assist sight or to correct defects in vision.
Classified arranged or distributed:in classes or according to class
CITATIONS
"Lens." Britannica Elementary Encyclopedia. Encyclopedia Britannica Online School Edition.

Encyclopædia Britannica, Inc., 2011. Web. 20 Sept. 2011.
Greivenkamp, John E and Hecht, Eugene.” Lenses (optics).”http://en.wikipedia.org/wiki/Lens_(optics). Wikipedia, Sept. 19, 2011. Web. 9/20/2011
Hewitt, Paul G. Practicing Physics. Boston: Pearson Addison Wesley, 2006. Print.
Dictionary.com. Dictionary.Reference.com, 2011. Web. 9/18/2011