# Day 47

Thursday, November 6

Physical Science: Today we took the Unit 2 Exam.

Chemistry: Today we took the Unit 2 Exam.

Physics of Light: Today was the bid discussion day. Students presented white boards on their converging lens lab. Below you can check out their white boards.

As you can see, most groups managed to figure out the important things. Such as the y-intercept is the inverse of the focal length (1/f). They also managed to see that (1/fh) + (1/fb) = (1/fhb). This is used to see what happens when you stack lenses together and combine their bending powers. It actually makes for a great way to introduce lens power (Power = 1/f in diopters when the units are inverse meters.) Basically power is a rating for how well the lens bends the light. The larger the lens power, the shorter the focal length, and the faster (shorter focal length) the light reaches the focal point.

We also talked about the meaning of the slope, as we always do. A lot of groups said it was the ratio of (1/di) to (1/do). When you look at the data though, one group said it best:

“We think it represents that as the (1/do) increases, (1/di) decreases at the same rate. So basically since it the inverse, as the object distance gets smaller, the image distance increases by the same amount.”

That would certainly explain  -1 slope. It also only works for situations where a real image forms…or maybe not. We still have to investigate and deal with virtual images at some point.

We did of course derive the thin lens equation as well. But more on that later.