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About "Ask A Scientist!"

On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.

Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.

Previous Week's Question Published: 17 April, 2003 Next Week's Question
No metal in the microwave: Aluminum foil isn't water
Question
Why can't you put metal in a microwave?

Question
Dear Sparking Chef,

When you look in a mirror, your image is bouncing off of metal. The back of a mirror is coated with aluminum. (Older mirrors were backed with silver.) Not only do metals conduct electricity, like when electricity runs through wires to lights and video games; they also reflect electrical waves that hit them from outside their surfaces. It may seem a little bit complicated, but I'd bet you've already seen it. Electricity runs through wires, and the wires are shiny. They reflect light. It's the way of the Universe.

The energy of light, heat, x-rays, radar, and in a microwave oven is what we call "electromagnetic" energy. It's electrical and magnetic at the same time. We can think of this energy as moving like a ray of light. We say it's "radiant." It "radiates." So, microwaves are "electromagnetic radiation." So is sunlight and heat and radar and television signals. They're all forms of the same thing. We have discovered that we can think of this electromagnetic radiation as traveling in waves. When the waves are short, they bounce off of metals, like light off of your mirror. When the waves are longer, they transfer energy into the metal, like the waves hitting a radio antenna on a car. Radio and television waves bounce off of you and trees and buildings and cars. Light waves are few tenths of a millionth of a meter long. Radio waves are a few meters long. That's quite a difference. Well, microwaves are somewhere in between. They're about 10 centimeters long, about as long your hand or a watch band unhooked. These waves are in between in how they behave around metals, too.

Microwaves happen to not pass right through water. Nor are they completely reflected by water. So, when we put something with water in it in the path of microwaves, say a potato or popcorn kernel, the water molecules start tumbling and jostling like crazy. The energy of the rubbing water molecules turns to heat. Your potato or popcorn heats up. When these waves hit metal like the aluminum foil or gold paint, the metal absorbs the microwaves like an antenna. The energy doesn't turn to heat, roughly because metal is not water. (You know that, too.) The microwave energy has to find a place to go. It usually forms sparks that jump from air molecule to air molecule all the way back to the metal sides or bottom of the oven. Where the sparks comes and goes from the aluminum foil or metal paint, it gets hot. The energy is concentrated. It often burns a tiny hole or pit in the metal. It's energy just looking for a place to spread out. It can't; so, don't put metal in a microwave. It's a bit like people who travel in waves at the speed of light. Wait maybe microwaves aren't like people. Oh well, they're part of our world just like you.