How Do Microwaves Heat Food?
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Radio Waves
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Microwaves contain tubes called magnetrons that convert magnetic and electrical currents into heat. When a microwave is plugged into an electric wall socket and turned on, the electricity reaches the center of the magnetron which causes it to produce electrodes. Electrodes work as conductors for electricity to pass through. Once the electric currents pass through the electrodes, they are converted into short radio waves. The magnetron transmits the waves out into the microwave where the water and fat in the food will absorb the waves. When the frequency of the radio waves is absorbed into the food, it begins to vibrate the water, fat and sugar molecules inside the food until it eventually becomes hot enough to begin heating the food.
Heat Penetration
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The heat waves from the magnetron heat food from the outside and can only penetrate to just over 1 inch deep. That is why thick or dense pieces of food will be hot on the outside, yet cold or frozen in the middle. In order to heat the very core of a piece of thick food, it must rely on the hot outside portions to conduct heat to it, which is why some microwave cooking instructions recommend removing the food to stir it before continuing to heat it. This helps distribute the heat so that the outside does not become burnt while you try to get the inside heated through.
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Standing Time
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Since the molecules in the food are vibrated so much by the radio waves that heat is produced, the vibration cannot come to a complete stop as soon as the microwaves turns off. After the microwave is done heating, the water and fat molecules in the food are still vibrating and keep heating the food until the molecules become cool enough to come to a complete standstill. The food can become hotter just in the time it takes to be put on a plate and served. Meats like turkey and roast beef are most prone to heating up by several degrees after they have been sitting. This is why some microwave food instructions advise to let food sit for at least 3 minutes to allow it to cool down.
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