Students set up a light bulb, a thin convex lens, and a piece of cardboard, in that horizontal order. They placed the cardboard so that an image of the bulb appered on it. Then they measured the distance from the bulb to the lens, and from the lens to the image.

image is the distance to the image.
bulb is the distance to the bulb.
group identifies which group of students. Their two lenses are different.

What is the relationship between the two distances? Is its form the same for both groups?

The groups did not report what units the distances were in (shame!). What do you think the units are?

If you know the thin-lens formula, do these data fit it? There is, of course, some variation. Do you think the "model" — the thin-lens formula — is within reasonable bounds of measurement error? What are likely sources of this error?

If you do not know the thin-lens formula, try plotting image vs bulb, and then combinations of changed data, for example, image^2, 1/image, etc., against one another. If you get a relationship that shows a straight line, you can figure out the "curved" relationship.

(data by students at San Leandro High School, courtesy of Mr Farley, Jan 2003)