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Lens equation

  1. Feb 11, 2013 #1
  2. jcsd
  3. Feb 12, 2013 #2
    We have chosen the sign convention to maintain consistency while solving the problems.

    Direction has been considered....
  4. Feb 13, 2013 #3
    I understand why we use sign convention ... but what's the need of using the sign convention once again ? We have already used the sign convention while deriving the formula for a lens.
  5. Feb 14, 2013 #4
    Perhaps, I am of the opinion that while deriving lens formula we use the concept of similar triangles and that formula : 1/f=1/v-1/u is sign independent for now, unless while solving the problems we consider the sign convention.

  6. Feb 14, 2013 #5


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    If you don't use a sign convention the how do you work out whether the image will end up in front of or behind the lens? Also, how do you distinguish between a concave or convex lens? (The answers to those questions are not allowed to include "you specify in words, which side and which type" - the calculation must involve just Maths.)
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