(classical music)
- Whether you love 'em or hate 'em,
there's no denying, microwave
ovens are super convenient.
They can heat food like
this much more quickly
than a conventional
oven, although not always
with the same results.
But how do they, you know;
how do they work, right?
Yeah, yeah, yeah, microwaves
sure, microwaves great.
But what the heck are those?
That's a good question.
Microwaves are a type of wave
on the electromagnetic spectrum,
and they're kind of
sandwiched, sanwiched...
between radio waves,
and infrared radiation.
In the case of microwave ovens,
the most common wave frequency
is roughly 2450 megahertz.
Waves in this frequency range
have an interesting property.
They're absorbed by
water, fats, and sugars,
and once they're absorbed,
they're converted
directly into atomic motion, heat.
These waves have another
convenient property though,
they are not absorbed by most
plastics, glass, or ceramics.
Metal, however, does reflect microwaves,
which is why it's a bad idea
to leave a spoon in your cheese dip
when the microwave oven's on,
not that any of us have done that.
You'll often hear people
say microwave ovens
cook from the inside out, right?
That's the key to the speed.
Well, think about it like this.
Let's say you are baking a
cake in a conventional oven.
Normally, you'd bake this at
350 degrees Fahrenheit or so,
but this time you
accidentally set that bad boy
for 600 degrees Fahrenheit.
The outside of the cake is gonna burn
before the inside even gets warm,
and you will have ruined
somebody's birthday.
In a conventional oven, the heat has to
migrate by conduction from
the outside of the food
toward the middle.
Hot, dry air on the outside
evaporates moisture,
so the outside can be crispy and brown,
you know, like the crust on bread,
while the inside is still moist.
In microwave cooking
though, the radio waves
penetrate the food, and excite
the water and fat molecules.
more or less evenly throughout.
Low heat has to migrate toward
the interior by conduction.
There's heat everywhere, all at once
because the molecules
are all excited together.
There are limits though.
Microwaves penetrate unevenly
in thick pieces of food.
That means they don't make it all the way
to the middle basically,
and there are also
hot spots caused by wave interference,
but you get the idea.
The heating process is different
because you are exciting atoms
rather than conducting heat.
Inside a microwave oven, the
air is at room temperature,
so there's no way to form a crust.
That's why microwavable
pastries or Hot Pockets,
sometimes come with
this little sleeve thing
made out of foil and cardboard.
The sleeve reacts to the microwave energy
by becoming very hot.
This exterior heat lets the crust become
as crispy as it would
in a conventional oven.
So that's it, that's the
secret behind microwaves.
Thanks to our producer
Paul for letting me eat
this Hot Pocket while we're recording.
(mumbles) What do you
think about microwaves?
Let me know in the comments;
do you love 'em, do you hate em'?
Let me know what other gadgets
you'd like me to cover
in upcoming episodes,
and check out our website
at howstuffworks.com
for more information and subscribe,
so you don't miss a moment of Brain Stuff.
