This Week's Experiment - #296 About Microwaves

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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