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Homework Help: Geomertical optics- derivation of graph of (u+v) against u

  1. Aug 23, 2014 #1
    1. The problem statement, all variables and given/known data

    may i know how to derive the the sha[pe of graph and get the point of min (2f , 4f) ? i really have no idea how to get the shape of the graph and the min point. The book give it without any explaination.

    2. Relevant equations



    3. The attempt at a solution
     

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  2. jcsd
  3. Aug 23, 2014 #2

    Simon Bridge

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    Do you have an equation that related u,v, and f?
    Put v=d-u, and solve for d.
     
  4. Aug 23, 2014 #3
    what equation is that? v=d-u i have only 1/u +1/v =1/f in my book
     
  5. Aug 23, 2014 #4

    Simon Bridge

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    1/u + 1/v = 1/f is a good place to start - that's the lensmakers formula.

    can you rearrange that equation to make v the subject?
     
  6. Aug 23, 2014 #5
    v= uf /(u-f) what shall i do next?
     
  7. Aug 23, 2014 #6

    Simon Bridge

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    OK - so if that is v, then v+u = ?
     
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