|How do microwaves work?
|Question Date: 2014-01-15|
Microwave ovens produce a type of energy that can
travel through the air, called radiation. Light
that comes out of light bulbs is also a type of
radiation, but we can see this visible light
radiation with our eyes. On the other hand, our
eyes cannot detect microwaves, so we cannot see
the microwave radiation shining down on our food
while a microwave oven is running. The best way to
think about a microwave oven is as a machine that
acts like a "light bulb" that produces microwave
radiation and shines that microwave radiation down
onto your food to heat it up.
The reason that microwave radiation is much better
at heating food than visible light is difficult to
explain. A simplified explanation is that
microwave radiation is very good at transferring
energy (heat) to water. Since most foods contain a
lot of water, this results in the transfer of a
lot of heat into your food. For some very complex
reasons, other types of radiation, like visible
light, are much worse at transferring energy into
water. As a result, we cannot just shine a normal
light bulb on food to heat it up quickly.
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Microwave ovens work by using 2.45 GHz frequency
electromagnetic waves know as microwaves to heat
the water in food. Water absorbs the energy from
the electromagnetic waves and turns that energy
into thermal motions causing the temperature of
the food to increase.
Side note: microwaves are
electromagnetic waves and as such are part of the
electromagnetic spectrum. Other examples of
electromagnetic waves include radio waves,
infrared light, visible light, ultra violet light,
x-rays, and gamma rays. The difference between all
of these electromagnetic waves are their
wavelength, frequency, and energy per photon.
Microwave ovens transmit a high power
electromagnetic wave into your food. It's the
same type of wave used for wifi internet
connections but at a much higher power level. The
microwave oven is shielded so that all of this
wave stays inside the microwave oven. The wave,
like all electromagnetic waves, consists of a
rapidly changing electric and magnetic field.
Most materials will absorb some energy from radio
waves, but anything containing water will absorb a
lot of energy because water is a polar molecule so
the molecules are easily jostled around by the
rapidly changing electric field. Heat is just the
random microscope motion and vibration of atoms
and molecules in a material, so when it is jostled
around by the wave it heats up.
Microwave is a color of light, too low-energy for
you to see, lower-energy even than infrared, but
higher-energy than radio.
Microwave ovens produce large amounts of this
light. Because of the size of the light waves
(micrometers, hence the term microwave), they are
capable of spinning water molecules as they go
past. This spinning of the water molecules then
rubs off on all of the other molecules they are
with, causing the entire substance to heat up.
A microwave oven uses microwave radiation to
heat water. A microwave oven produces microwave
radiation with a frequency of about 2.45 GHz,
which is similar to a cordless phone or your wifi
router. However, the radiation is much more
intense, so when this large amount of energy is
transferred to water molecules in your food, it
causes the food to heat up. Specifically, the
microwave radiation causes water molecules to move
around, and when they bump into other molecules,
they transfer this energy in the form of heat.
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