(Sorry to bother you with a dumb question.)
I bought an used microwave oven. Turns out that it's not quite in working order. I've tested it a few times now: it heats the containers/plates, but not the food. I can't even melt a piece of chocolate in it.
I just tried to heat up a burger. After four minutes in the oven the plate feels hot, but the burger is still refrigerator cold. I'm pretty sure that's not supposed to happen.
I thought I knew how microwave ovens work, but... evidently not. How can it heat the dishes without warming the food? I used the same plates in my old oven and they never got this hot.