1. Not finding help here? Sign up for a free 30min 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!

Find the change in focal length

  1. Mar 26, 2009 #1
    1. The problem statement, all variables and given/known data
    A nearsighted person has eyeglasses with a -1D prescription. If the near point is at 23 cm without eyeglasses, where is it when they are put on?



    2. Relevant equations
    (1/f)=(1/do)+(1/di)


    3. The attempt at a solution
    I got the answer which is 0.298701298 meters by -1= (1/do)-(1/0.23)...but the problem is that i don't know why it's like that...Any ideas would be extremely helpful!! Thanks!!
     
  2. jcsd
  3. Mar 26, 2009 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Re: lenses

    You have that equation wrong,
    f = the focal length of the lens ( -0.23m)
    di is the image distance (which you don't know - but can assume is the same )
    do is the object distance

    Then you need the formula for a combination of two lenses (ie the eye + glasses) to find the change in focal length.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Find the change in focal length
Loading...