This lab is based on a paper on the subject from AmJ. As the final lab of the PHYS140's sequence I have the following goals:

• Provide the experience of reading a journal paper and conducting an experiment based on it.
• Using a model to describe the expected behavior of the phenomena, and then using that to sanity check observations made during the experiment.
• Understanding that there any model for a phenomena has underlying assumptions baked into it, recognizing these assumptions and taking them into consideration while figuring out how to do the experiment.
• Demonstrating some “interesting” aspects of how sensors, including the human eye impact what you observe.

I want students to read the paper before coming to lab. To do this I ask the TA's and faculty to distribute the paper to the students during the week before the lab, and inform them that there will be a 5 minute quiz on the content of the paper at the start of the lab. The quiz is only there to motivate students to read the paper before the start of lab. Nominally I assign 1 point out of 8 for the quiz, but I tell TA's not to even bother grading it. The point is not how many right answers do they get, the point is having read the paper.

The quiz itself consists of 4 T/F questions which are trivial if you have read the paper. I tell TA's to give the students 5 minutes at the start of the class for the quiz. The questions are:

1) The sequence of colors produced by thin film interference is the same as what you see in a rainbow. (F) 2) The color sensors in the human eye and a digital camera both record light as Cyan, Magenta and Yellow values. (F) 3) Where the film is very thin (<50nm) all reflected wavelengths interfere destructively and there is no reflected light. (T) 4) The color of the reflected light depends on the thickness of the film. (T)

Students have seen interference, so the basic physics does not have to be presented by the TA. They should however be prepared to go over addititive color mixing as it applies to camera sensors and the human eye, both of which have R, G & B color sensors. An interesting aspect of this is that we (humans) perceive colors that do not exist in nature in the sense that they have no wavelength. Magenta for example is a mix of red and blue and does not appear anywhere in the spectrum of light. But since the camera and our eyes both combine information from R, G & B color sensors, we perceive magenta as a color.

To emphasize this fact I ask students to google a picture of a rainbow or white light spectrum and compare the colors and they sequence to what appears from thin film interference (TFI). This is a qualitative show & tell exercise, but I want them to notice that while the TFI pattern might at first appear to be the same as the visible light spectrum, they are not the same.