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Microwave

✨ The heat box

A microwave oven heats food by using electromagnetic waves called microwaves. In most household ovens, a magnetron generates waves at a frequency of about 2.45 gigahertz. These waves enter the food and interact especially strongly with polar molecules, such as water. As the electric field changes direction extremely rapidly, these molecules tend to rotate and move. Their motion increases the internal energy of the food, which raises its temperature.

Dissolved ions and other components can also contribute to the heating process. Despite a common misconception, microwave heating is not simply caused by water molecules "resonating" at one particular frequency. The waves penetrate the food to a limited depth, so heat is also redistributed through ordinary conduction. The amount of heating depends on the food's composition, shape, moisture content and position in the oven.

The oven's metal cavity reflects microwaves and keeps most of their energy inside. Many models use a rotating turntable or another system to reduce uneven heating, since microwave fields can form areas where heating is stronger or weaker. The food may therefore contain hot and cooler spots, especially when it is thick or irregularly shaped. Microwaves do not make food radioactive; they are non-ionizing radiation and do not have enough energy to cause nuclear changes.

Metal objects can reflect microwaves and may produce electrical discharges in certain situations, which is why the manufacturer's instructions should always be followed. Containers designed for microwave use allow the waves to reach the food while tolerating the heat produced during cooking. The oven heats the food directly through microwave energy, but the final temperature can still become more uniform as heat spreads inside the food.

💡 Did you know?

Did you know that the microwave was invented thanks to a chocolate bar? In 1945, engineer Percy Spencer was working on radars when he noticed that the chocolate in his pocket had melted! He realized that the radar waves had heated his snack, and that's how he got the idea to create the microwave oven.

Why should you never put metal in a microwave? The oven's waves bounce very hard off metal instead of passing through it. This creates electrical currents that cause large sparks to fly, a bit like small lightning bolts! That's why we only use glass or special plastic.

The very first microwave marketed in 1947 was a real giant! It was almost 2 meters tall and weighed over 300 kilos. It was also very expensive. Today, they have become very small and can fit on your kitchen shelf!