Can papper catch on fire in the microwave?

Answer 1

Yes, however it is difficult. It is unlikely that a single sheet of paper will catch fire, however, a stack of paper may. Also, a tightly, crumpled ball of a single sheet of paper can catch fire, whereas if it is loosely crumpled it is unlikely to catch fire. In the first case, a single sheet will not be able to capture enough microwave energy in order to heat, and also, it's very large surface area to weight ratio means that it will lose any heated gained very quickly to the cool outside.

In the case of the crumpled ball, the three things that are necessary for fire to occur are a fuel, a source of ignition, and oxygen. When the ball is loosely crumpled the sheet may heat somewhat but it can't concentrate enough fuel in order to catch fire. However, if the ball is tightly crumpled the fuel can be concentrated and ignited.