# Applied Physics and Chemistry Refraction Lecture 5.

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Applied Physics and Chemistry Refraction Lecture 5

Refraction Definition: Bending light due to change in speed Index of refraction: Relative amount that the material bends light Ratio of speed of light in medium compared to speed in a vacuum

Lenses Lens is: Curved transparent material that bends light to a focus Light bends toward thickest part Two kinds: Concave Convex

Concave Lenses Lenses that are thicker at the edges and thinner in the center. Diverges light rays All images are erect and reduced. The De-Magnifier

Concave Lenses Two rays from top of object define image location http://homepage.mac.com/cbak ken/obookshelf/ccimages.html

Equations All lenses obey the same equation 1/do + 1/di = 1/f f is negative for concave lens di is also negative Magnification: hi/ho = di/do

Example Joe bought a concave lens having a focal length of -10 cm. He placed a lighted object 30 cm in front of the lens. Where will the image be formed? What type of image will it be? What we know: f = -10 cm Do = 30 cm Di = ? Equation: 1/f = 1/Do + 1/Di Solve: 1/Di = 1/f - 1/Do = (1 / -10 cm) - 1 / 30 cm = -4 / 30 cm = -0.1333 cm-1 Di = -7.5 cm The image is upright, reduced and virtual