# Thin Lens Experiment

1. Sep 22, 2004

### Kalashnikov

Hi,

I'm first year Engineering in the Phys1130 course at my college and I've ended up hitting a large brick wall with the pre-lab. The pre-lab section of the experiment goes:

"The thin lens equation is:

(1/do) + (1/di) = (1/f)

di = distance from lens to image
do = distance from lens to object
f = focal distance from lens

Now, the pre-lab asks to prove that the plot of (dodi) vs (do + di) is linear and to determine what the slope and intercept are predicted to be.

Show that if two lenses (f1, f2) are placed together (assume distance between them is 0), the equivalent focal length of the system is given by:

(1/f) = (1/f1) + (1/f2)"

Alright, for the first half of the pre-lab I have rearranged the forumla, added the intercept value of 'b' to the end of the equation but cannot seem to find out how to prove that its a linear graph. I know it should be, but I cannot find a way to communicate that across. The slope and intercept is also a mystery to me because we are given no values to calculate them with, unless of course the most we can do is algebra calculations.

the forumla became: dodi = f(do + di) + b and from here I do not understand how to determine these values of slope and intercept as well as prove its a linear graph. Any hints or help would be GREATLY APPRICIATED

The second half of the pre-lab is almost blowing my mind. I was fairly confident I knew what I was doing, substituting in values for f1 and f2 and others, but I'm feeling almost nausiated thinking about other ways and whether or not my way is correct.

2. Sep 22, 2004

### vsage

Compare the units of d0 + di and (d0*di).

Last edited by a moderator: Sep 22, 2004