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B Math in the thin lens equation

  1. Jun 2, 2016 #1
    Why isn't 1/f=1/do+1/di just the mathematical equivalent to f=do+di? Can't you raise all terms in the equation to the power of negative 1 to get the latter equation? The maths of reciprocals is confusing me lol.
  2. jcsd
  3. Jun 2, 2016 #2
    That is not the lens eqn.
    The lens equation is :- 1/f = 1/v - 1/u
    Where v:- image distance with sign convention
    u:- object distance with sign convention
    just take reciprocal of whole eqn

    ## \frac {1}{\frac{1}{f}} = \frac {1}{\frac{1}{v} - \frac{1}{u}} ##

    ## f = \frac{1}{\frac{(u-v)}{uv}} ##

    ## f= \frac{uv}{u-v} ##

    Clearly it is self explanatory.
  4. Jun 2, 2016 #3
    Kuzon has written a perfectly acceptable version of the lens equation, one that is commonly used.

    Kuzon: raising to a power does not follow a distributive law as does multiplication. So we have a(b + c) = ab + ac but (b + c)2 ≠ b2 + c2.
  5. Jun 2, 2016 #4
    Sorry, I did not know that version of lens equation; as in our country the lens equation version used is different.
  6. Jun 2, 2016 #5
    I have acquired the same as @Sahil Kukreja . The relation is about their reciprocals, and cannot directly be changed to what @Kuzon wrote.
  7. Jun 2, 2016 #6
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