英语时差：微波炉如何加热食物？2

Microwaves heat water by jerking the water molecules around, so to speak. Each water molecule has a slight positive electric charge on one side and a slight negative charge on the other. As microwaves pass by, they exert forces on those charges, first one way, then the other, several billion times per second. These back-and-forth forces turn the water molecules one way, then the other, repeatedly breaking the temporary bonds that water molecules form with each other. It’s a kind of microscopic stirring. The result of all this agitation is more violent random motion of all the water molecules in the food — in other words, the water gets heated. Microwaves reach all the water in the food at once, so all parts of the food are heated at once. A conventional oven heats food only from the outside, and that’s why conventional cooking takes longer than microwave cooking.