Microwave ovens employ a device called a magnetron that emits electromagnetic waves (“microwaves”) that oscillate billions of times per second, causing water molecules (and, to a lesser extent, oil molecules) in the food to move at the same incredibly fast rate, increasing their temperature.
Here’s the catch: In most microwave ovens, because the magnetron is designed to emit a single wavelength, the intensity of the radiation can’t be altered. It can, however, be turned on and off, and that’s exactly what power levels do. When you lower the power level in a microwave oven, you decrease the amount of time the magnetron stays on. To see this phenomenon in action, we grabbed some LED light bulbs (which also respond to microwaves) and did some experimenting.