The electromagnetic spectrum can be difficult for students to understand because they can't see the waves. Furthermore, students don't always understand the relevance of these different wave types and that they fall along a continuum.
In this PBL, students are given the problem of designing posters of the Milky Way Galaxy photographed at different wavelengths. They must not only design posters, but also provide a description of the important characteristics provided by the photograph at a particular wavelength.
This PBL will not only help students conceptualize and assign relevance to the electromagnetic spectrum, but also will reinforce that it is a continuum of waves with different characteristics. This activity will last 2-3 days depending on how much time you want to give students to complete the research and posters.