Power in a pathways can be switched to another pathway by a device, here the source, absorber and detector are all devices, making the link with teaching about energy and power.
By varying the materials between source and detector you can model macroscopic behaviours (Again, engineering the space between source and detector).
Get an interesting (exponential) pattern from iserting successive slices of absorber between source and detector. There is an exponential relationship between acticities, the powers absorbed, and the powers transmitted.