This Week's Experiment - #296 About Microwaves
This week's experiment came from a question asked by a student during my
energy show. He wanted to know how microwave ovens work. For this
experiment, you will need:
3 identical, microwave safe containers
water
cooking oil
a microwave oven
I used small drinking glasses, but any microwave safe containers should work.
Put about an inch of water into one glass, about an inch of cooking oil
into another and leave the third glass empty. Place all three glasses into
the microwave oven. Set the time for 15 seconds and start the oven. When
the oven stops, open the door and carefully remove all three glasses.
Carefully feel the outside of the glass of water, at the water level. It
should feel quite warm. Making sure not to burn yourself, carefully touch
the surface of the water. It should also be quite warm, possibly even hot.
Do the same thing with the glass of cooking oil and the empty glass. What
do you notice?
The glass of water heated up nicely, but the glass of oil, and the empty
glass did not. Why? It has to do with how a microwave oven works.
Inside the oven is a tube called a magnetron. This magnetron broadcasts
microwave radiation. RADIATION!!!! Oh, no! Is my food radioactive?
No. There are many kinds of electromagnetic radiation, such as radio,
television, radar, and light. Microwaves do not make your food radioactive.
So how to the microwaves cook your food? They cause the water molecules in
the food to vibrate. Why just the water molecules? Water molecules are
polar. That means that one end of the water molecule has a positive charge
and the other end has a negative charge. As the name suggests, microwaves
are waves. They are not waves of water, but waves of electromagnetic
energy. Just as a wave in water can cause an object to bob up and down, the
microwaves can cause a molecule of water to vibrate first one way and then
the other. As the wave approaches the molecule, the positive end is pulled
one way and the negative end is pulled in the opposite direction. As the
wave passes, the pulls are reversed. This causes the water molecule to
vibrate back and forth rapidly, which makes it hot. The water molecule then
passes some of the vibration to surrounding molecules, making them hot too.
Oil is not a polar molecule. That is the reason that oil and water do not
mix easily. Polar molecules stick to other polar molecules, but not to
nonpolar ones. Because the oil is not polar, it is not heated by the
microwaves. That is why we cannot fry things in the microwave. But wait a
minute. I have had bacon cooked in the microwave. What about that? The
bacon contains water as well as the fat. The water in the strip of bacon
provides the heat to cook it. The fat just drains away. It will be hot,
having been heated by the water in the bacon, but it will not continue
heating once it drains away.
Dry foods do not cook well in the microwave oven. Remember that the empty
glass did not get hot. You need the polar molecules in the water to get the
heat for cooking.
Now, lets get back to the RADIATION. You might have heard that microwaves
change the chemical structure of the food. Yes, cooking food with
microwaves does change the chemical structure of the food. So does any kind
of cooking. That is the reason we cook food. If you don't want the
chemical structure of your food changed, eat it raw. Food cooked in a
microwave oven is just as nutritious as food cooked by other means. It is
not radioactive and not dangerous, as long as you don't burn yourself with it
or drop it on your foot. On second thought, if you count eating too many
microwave brownies as dangerous, then you could count my microwave as a
hazard area. Have a great week.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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