Microwaves
are basically extremely high frequency radio waves, and are
made by various types of transmitter.
In a mobile phone, they're made by a transmitter chip and
an antenna, in a microwave oven they're made by a "magnetron".
Their
wavelength is usually a couple of centimetres. Stars also
give off microwaves.
Uses
Microwaves
cause water and fat molecules to vibrate, which makes the
substances hot.
So we can use microwaves to cook many types of food.
This
YouTube video clip gives you the idea...
Mobile
phones use microwaves,
as they can be generated by a small antenna, which means that
the phone doesn't need to be very big. The drawback is that,
being small, they can't put out much power, and they also
need a line of sight to the transmitter. This means that mobile
phone companies need to have many transmitter towers if they're
going to attract customers.
Microwaves
are also used by fixed traffic speed
cameras, and for radar,
which is used by aircraft, ships and weather forcasters.
The most
common type of radar works by sending out bursts of microwaves,
detecting the "echoes" coming back from the objects
they hit, and using the time it takes for the echoes to come
back to work out how far away the object is.
Dangers
Prolonged
exposure to microwaves is known to cause "cataracts"
in your eyes, which is a clouding of the lens, preventing
you from seeing clearly (if at all!) So don't make a habit
of pressing your face against the microwave oven door to see
if your food's ready!
Recent
research indicates that microwaves from mobile phones can
affect parts of your brain
- after all, you're holding the transmitter right by your
head. The advice is to keep calls short.
People
who work on aircraft carrier decks wear special suits which
reflect microwaves, to avoid being "cooked" by the
powerful radar units in modern military planes.
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