# Physics and Astronomy Labs/Optics: Thin lens equation (ray diagram)

- Each student makes a drawing similar to figure below and measures S
_{1}, S_{2}, and f. Enter those values on a spreadsheet, making columns for each entry. - To the right of this column, create three more columns that contain: S
_{1}/f, S_{2}/f, and f/f (each entry in the last column is of course. These three columns represent the image and object distances, as measured in**unity***focal lengths*. - Let
*x*= S_{1}/f and let*y*= S_{2}/f, and make a plot of x versus y. - Now make a plot of X=1/x and Y=1/y. When doing such calculations by hand, use "bars" to distinguish upper and lower case letters, as shown to the right.
- S
_{1}represents the "object distance". Carefully define this distance by fully describing the two endpoints. The formula is only valid for an infinitely thin lens, research which part of the lens is used to define this endpoint. Research the Wikipedia articles and see if you can find a place where this distance is defined. The best way to search Wikipedia is NOT the Wikipedia search bar. Use Google or its equivalent instead. A list of search words includes*thin lens*and*paraxial approximation*

relates the focal length *f* of the lens, the image distance *S _{1}*, and the object distance

*S*. The figure depicts the situation for which (S

_{2}_{1}, S

_{2}, f) are all positive: (1)The lens is converging (convex); (2) The real image is to the right of the lens; and (3) the object is to the left of the lens. If the lens is diverging (concave), then f < 0. If the image is to the left of the lens (virtual image), then

*S*.

_{2}< 0**If Wikipedia fails to answer this question**:- Search the internet for the answer to this question.
- Find a place in Wikipedia where this information should be inserted.
- Choose an editor among the class who will do the deed. Be sure to follow Wikipedia's policy on
**meat puppetry**