Help_How to use graph to find focal length?

1. Jan 10, 2010

linda92

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. Jan 10, 2010

tiny-tim

Welcome to PF!

Hi linda92! Welcome to PF!

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 … ?

3. Jan 10, 2010

linda92

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 :)

4. Jan 10, 2010

Woohoo!