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Q & A: Spoon images

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Most recent answer: 07/11/2011
i have read your answers to the many questions of why our reflection is upside down in the spoon. but why is it only upside down on the front part of the spoon and not the back of the spoon.
- darren (age 21)
The curved surfaces of a spoon act like mirrors.  The front part of the spoon is concave while the back side of the spoon is convex.  The usual formula for a lens is 1/d0 + 1/di = 1/f  where d0 is the object distance, di is the image distance and f is the focal length for the mirror. The value of f is positive for concave mirrors and negative for convex mirrors.  If you do some ray tracing you find an image reversal for concave mirrors but not for convex.   
Take a look at for some explanatory diagrams.


(published on 07/11/2011)

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