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!

Homework Help: Help_How to use graph to find focal length?

  1. Jan 10, 2010 #1
    1. The problem statement, all variables and given/known data
    Rearrange the lens equation to make 1/v the subject of the equation and then write it as a linear equation. This will lead you to a possible graph for data of object distances and image distances from which you will be able to evaluate the focal length f of the convex lenses.

    2. Relevant equations
    *lens equation: 1/f=1/u+1/v

    3. The attempt at a solution
    I don't really understand what I'm supposed to do. I mean, usually we have equations like y=kx and all we do is to find the slope k. But for the equation 1/v=1/f-1/u ? I really don't get this. Should I make it into v=uf/(u-f)? I think that's the right way but I dont know if i can get f using that equation. Please HELP!
     
    Last edited: Jan 10, 2010
  2. jcsd
  3. Jan 10, 2010 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi linda92! Welcome to PF! :wink:

    You want a straight line,

    so instead of having v along one axis, you have 1/v instead.

    And along the other axis, you have … ? :smile:
     
  4. Jan 10, 2010 #3
    Re: Welcome to PF!

    Hello! Thanks :)

    The other side I made it 1/u.
    In Graphical Analysis I entered the function "f(x)=1/f-x", with x=1/u, f(x)=1/v..

    ...And it worked :)
     
  5. Jan 10, 2010 #4

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    :biggrin: Woohoo! :biggrin:
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook