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How microwaves cook food
The frequency of microwaves used in
microwave ovens is set by the FCC at about 2500 MHz. It is set
here so as not to interfere with radio waves of other frequencies used
in communications. This frequency also has 3 very important
properties.
1) Microwaves are reflected
by metal, like light rays are refl ected from a mirror.
This means that the microwaves are contained inside the oven because
the walls
are made of metal.
2) Microwaves can pass
through plastic and glass which also turns out to be quite
convenient, because that way they can pass through the container that
the food is kept in, and be absorbed by the food instead.
3) Microwaves are absorbed
by water, oil and sugar molecules and those are the kinds of
molecules in foods.
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What does it mean that microwaves are absorbed by a molecule? It
means that the energy is transferred to the molecule, making it move
more, so the temperature of the food rises. Think about an
X-ray. It can pass through skin, and then is absorbed by
bone. In the same way microwaves pass through the glass cup, and
are absorbed by tea. In very thick foods, sometimes the
microwaves cannot reach the middle of the food, since they have been
absorbed by the outer edges, so it is advisable not to cook very thick
foods in a microwave oven.
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