1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    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.)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook