How a microwave oven heats food, and why the middle stays cold
Is microwave radiation safe? Why microwaved food never becomes radioactive
"Microwaves are radiation" is true, and it scares many people away from their own kitchen. But radiation is a big family, and microwaves are among its weakest members. Find out what they can and cannot do to your food, and how the door keeps them inside.
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1
Miva is right that microwaves are radiation. But radiation just means energy that travels out from a source. Radio, microwaves and light are all radiation, and they travel as waves. Microwaves sit next to radio, far weaker than light.
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2
On their own, microwaves can only make molecules turn. Food becomes radioactive only when the cores of its atoms change, and microwaves are far too weak to touch them.
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3
And nothing stays behind. When the magnetron stops, the waves are gone in a tiny moment, like the light in a room when you switch off the lamp. All that is left in the chocolate is heat.
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The waves cannot get out, either. The window of the door has a metal sheet full of tiny holes, about a millimetre wide. A wave about 12 centimetres long cannot get through them. Light waves are far smaller, so you still see your food.
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5
So Miva takes a piece after all.
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6
But something counted Rono's 20 seconds and beeped at the end. Something also switched the magnetron on and off for Miva's defrost. A small computer hides behind the keypad. Meet it, and the many others in your home, in "How embedded systems work: the hidden computers in everyday things, and how engineers build them".
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Quick check
A Wi-Fi router.
Show the answer
No. Its waves are the same weak kind, so they can only make molecules turn. And a router sends out far less power than an oven, about a ten-thousandth, far too little to warm your food.
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Go further
Rays, doors and Wi-Fi.