We apply the principles of the electromagnetic spectrum, electricity, magnetism, and molecules. When the AC power comes into the microwave oven, first it goes through some safety switches. Then it goes into a high volt transformer. This is a “step up” transformer, that changes the voltage from 115-120 volts to over 3000 volts.
The magnetron uses electricity to generate microwaves at a frequency that interacts with molecules in food. Food molecules - particularly the water molecules in food - have a positive and negative end in the same way that a bar magnet has a north and south pole. The microwaves change polarity from positive to negative with each cycle of the wave. These changes happen billions of times every second. When microwaves at the right frequency hit the food, they cause the molecules in the food to vibrate at the same frequency as the microwave, billions of times per second. The moving molecules create friction in the food, which heats up the food. (Remember, friction produces heat - try rubbing your hands together to warm them up.)
Since food surfaces vary, and some pieces of food are thick, the microwaves don’t necessarily heat the food evenly. Some ovens have a stirrer blade which attempts to distribute the microwave energy evenly in the oven. Most now have a rotating turntable which rotates the food in order to allow more even distribution. You’ve probably noticed that microwave ovens cause bread to become soggy, and they don’t bake bread well. This is because conventional ovens depend on conduction to cook the food. The outside of the food receives more heat than the inside. This allows breads to become crusty. Microwave ovens, since they work by exciting molecules, not conduction, don’t allow this. The air inside a microwave oven is at room temperature.
Microwave Oven
What heats up the food in a microwave oven?
Microwave ovens take advantage of the behavior of water molecules when subjected to electromagnetic waves found in the microwave band. The food is heated by moving these molecules in the food – creating friction – thus heating up the food.
Microwaves
Waves in this frequency range are absorbed by ________.
They are not absorbed by ________.
They're absorbed by water, fats and sugars.
They're not absorbed by most plastics, glass or ceramics.
