I recently purchased a new microwave oven, and there's a metal rack in it. The salesmen informed me that it shouldn't cause any problems as long as it didn't touch the sides; however, he was unable to tell me why this is. I have a basic understanding of how microwaves(as in the radiation not the ovens) interact with polar molecules causing heat and how they interact with delocalized electrons, and I can't think of an explanation as to why not touching the sides would prevent this interaction from occurring. Well, that's a lie; a more accurate statement would be that I cannot think of a satisfactory explanation. Any thoughts?