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posted by  ItxguyI on 7/28/2008 1:54:26 PM  |  status: Live  

desperate for help, will rate well

Course Textbook Chapter Problem
General Physics N/A N/A N/A
Question Details:
A section of a sphere has a radius of curvature of 0.68 m. If this section is painted with a reflective coating on both sides, what is the focal length of the following sides? (Include the sign of each answer.)
(a) the convex side
cm
(b) the concave side
cm
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Oracle
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posted by Steve (retired) on 7/28/2008 3:42:55 PM  |  status: Live
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ItxguyI's comment:
"thnx"
Response Details:
The focal length is
 
 a) f = - (1/2)R = .....cm
 
b)  f =  (1/2)R = ......cm


The focal length is equal to half the radius. Focal length of the convex mirror is always negative because it is behind the mirror. Focal length of the concave mirror is always positive because it is in front of the mirror. Imagine a sphere, the inside makes up the concave lens while the outside makes up the convex lens shape. Looking inside towards the out, we see the concave side, thus the focus is within this area (in front of the lens). Whereas, looking from the outside towards the inside, the convex lens appears with the focus inside the sphere, thus behind the mirror
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