Today, everyone knows it: metal objects should not be put in a microwave oven. This may damage the oven or even injure the user of the appliance. But why ?
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[EN VIDÉO] Kezako: the surprising operation of the microwave oven To quickly heat up your meal, nothing is more practical than the microwave oven. This invention derived from radars does not use heat to heat food, but a much more surprising process. Unisciel and the University of Lille 1 explain to us, with the Kézako program, how the microwave oven works.
To understand why it is better to ban metal objects from microwave ovens, let us first recall some basics of operation of these devices. If they reheat food with such efficiency, it is because they generate electromagnetic waves whose specific frequency vibrates the molecules of water present in said foods.
This microwave frequency is 2.45 GHz, which is slightly below the frequency of the light visible. And the turmoil it induces within the water molecules is sufficient to produce heat.
Microwave oven: the shape more than the material
Metals, on the other hand, as electrical conductorswear electrons free who move within the metal under the effect of these same electromagnetic waves. And they will focus on the roughness and other points that the object presents. When the charge concentration exceeds at these places, the breakdown value of theairthe latter ionizes and there is formation of an electric arc generatingozone and of NOx.
The heat released by these arcs reaches several thousand degrees and can therefore start a fire inside the microwave oven. However, today there are containers, in aluminum in particular, whose shape is designed to avoid electric shocks.
Note also that in a microwave oven, metals behave like mirrors and reflect the waves, preventing them from reaching the food to heat it. And by reverberating on the walls, the waves end up damaging the components of the oven.
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