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Homework Help: Lens silvered at one face

  1. May 13, 2012 #1
    1. The problem statement, all variables and given/known data
    Its not a specific question but a general one to solve similar questions. I need to find focal length of a lens silvered at one face

    2. Relevant equations

    3. The attempt at a solution
    I know a convex lens silvered at one face will behave as an effective concave lens. But i need to find the equations. I can do it by individually solving each case but need a faster one.
    My book says that the effective power, P = P(L) + P(M) +P(L).....P(L) is power of lens P(M) is power of mirror. I dont know why this works?

    For two lenses kept close i understand why P = P1 + P2 but don't how this works in lens-mirror case too.
    Any Help?
  2. jcsd
  3. May 13, 2012 #2


    User Avatar

    Actually it does. Just do it logically. I think that powers add because of formula being 1/v -1/u , so when you add p2 the image of 1 is oblect for 2 so basically it cancels out .p1 +p2 is just using the lens formula ignorantly . Ensure that proper sing and conditions are followed.Hope that helps
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