Now is the time to make it more quantitative. Under many circumstances this would imply that we were about to whip a little math on the problem to make it more cooperative. While its true that in the long run you gotta do the math even in optics, there is a great deal that can be learned about the situation from simple sketches. Much of the reason for this has to do with our ability to integrate large amounts of information visually. Mathematics communicates to most of us along a single channel.
Pictures activate many information channels simultaneously.
In the case of optics these pictures are fairly accurate representations of the physical world which makes them more meaningful. Most scientists who work with optics do a great deal of their basic thinking using some variation of model you are about to learn. Only after they have done their graphical thinking do they refine it with mathematics. Sorry that this discussion is so brief but this new lab is being developed on the fly to better integrate with our curriculum this year.