In physics we are currently looking at image formations with a plane mirror. After concluding our Pane Mirror Lab, and learning how to create basic plane mirror diagrams, the students were introduced to more complex systems.
The kids then drew up their diagrams, and shared them in class. I have found that trying to create white boards of lens/mirror diagrams is problematic. So to alleviate the stress, I use my iPad as a document camera, and project their homework onto my SMARTBoard with an AppleTV.
The kids, through observing the actual setups, were able to determine that the image formed in one mirror was acting as the object for a second mirror. This mirrors (pun intended) what we observe for double lens systems, which the kids are already fully familiar with.
I also like the method of teaching the lens material before the mirrors. Lenses form aerial images or real images, which the students can see in the lab. The fact that light rays come together to form images, is more concrete than going into mirrors first. Most images formed by mirrors are virtual images, and conceptually they pose a much larger problem for students to understand.
At this point in our Light course, we have fully developed how real images form, and in the process of studying lenses, they were given a concrete method of discovering virtual images. By seeing the lens action, and how it leads to virtual images leaves a better impression, than simply defining the virtual image formed by plane mirrors, and hoping that the students get a firm traps of the concept.