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# Mirrors

Module by: Paul Padley. E-mail the author

Summary: We come up with the mirror equation.

Notice that in Mirrors we get a virtual image to the right of the surface. Thus for mirrors we say that s i s i is positive to the left of the mirror. This allows to retain correspondence between s i s i being negative and an image being virtual.

Again we use the small angle approximation. By inspection of the figure we see that 2 θ i = α + β 2 θ i = α + β and θ i = α + γ . θ i = α + γ . Now we multiply the second equation by two and subtract the first equation from it and we get: 2 α + 2 γ α β = 0 2 α + 2 γ α β = 0 or α β = 2 γ . α β = 2 γ . Using the small angle approximation we see that this is h s o + h s i = 2 h r h s o + h s i = 2 h r where I have used the fact that s i s i is negative to the right of the mirror. So I can write the mirror equation as 1 s o + 1 s i = 2 R 1 s o + 1 s i = 2 R or 1 s o + 1 s i = 1 f 1 s o + 1 s i = 1 f where for a mirror 1 / f = 2 / R 1 / f = 2 / R

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##### Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

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