A dry aluminium foil paper can be bring out from oven with no burn on finger but if foil has some moisture it will result in burn why?
It isn't the foil that is burning you--it's the water. Aluminum foil is a good heat conductor. This means that when you expose the foil to the air, it will cool off very rapidly (rapidly reaching room temperature). Water is NOT a good heat conductor, in fact, it likes to hold onto it's heat. So while the dry foil may come to room temperature (or just warm to the touch) in a few seconds, the water will stay hot for much longer (depending on how much water there is obviously). It's really the same as trying to grab a baked potato wrapped in foil off of the grill. If you grab the potato you will burn your hand (because the potato is holding A LOT of heat), but if you carefully peel away the foil, you can touch and take the foil off with your bare hand. I should say that the mass of the foil also plays a role here. The foil is not very massive and thus does not hold a lot of raw energy to begin with (also because it's a good heat conductor it dissipates quickly). Bu if you put an aluminum can (or a brick of aluminum) in the oven, I guarantee that it would stay hotter for much longer than just a piece of aluminum foil.
The Principle behinf Microwave oven heating is that it heats up only water molecules, that is, the frequency of microwaves can only heat up water molecules ( make them oscillate and hence heat up). So if there is any trace of water or moisture on any object that you keep in the oven, it will heat up and that heat will be conducted throughout the object. Hence the foil with moisture is effectively heated whereas dry foil have no water moecule and hence will not be heated up. Hope it helps:) Can explain better if you tell me which level you are studying:)
