Science Projects, Lesson Plans and Experiments
This Week's Experiment
#473 Microwave Ice
A very Happy New Year to everyone. Nancy and I had a marvelous holiday, and
now we are preparing to head south to Ft. Pierce, Florida for more school
shows for Florida Power and Light. During our time off we visited with friends,
drank lots of eggnog, took tons of photos with the new lens Nancy gave me for
Christmas, drank lots of eggnog, worked on quite a few projects around the
house, drank lots of eggnog, stayed up all night for a couple of DVD movie
marathons, and of course, drank lots of eggnog. I love this time of year!
This week's experiment is a result of defrosting some frozen food. Have you
ever wondered why there is a defrost setting on your microwave? Why can't
you just use the regular setting? To find out, you will need:
2 glasses
water
ice cubes
a microwave oven
Fill one glass about half full of water. Fill the other about half full of
ice cubes. Work quickly, as you don't want any of the ice to melt before you
start. Put both into the microwave oven and cook both at full power for one
minute. Carefully, because things may be very hot, remove both glasses from
the oven. You will find that the water is quite hot, but the ice will not
have melted at all. Why?
Your microwave oven works by directing microwave radiation at your food.
Radiation! Is my food going to glow in the dark? No, here radiation means
radiant energy, which includes visible light, radio signals, microwaves, and the
rest of the electromagnetic spectrum.
As we have seen in the past, water molecules are polar. One end of the
molecule has a positive charge, and the other end has a negative charge. The
water molecules rotate to align with the alternating electric field produced by
the microwaves. As they rotate quickly back and forth, the water gets hot.
With the ice, the water molecules are locked into position. Since they
can't rotate back and forth, they do not convert the microwaves into heat. Then
how can the microwave oven defrost food? Put a fresh glass of water into the
oven and set it on the defrost setting. Cook the water for 30 seconds,
paying attention to what the oven is doing. You should hear the sound changing
as the oven cycles on and off.
On the surface of the frozen food, some of the ice will begin to melt at room
temperature. The microwaves will cause this tiny bit of water to get hot.
Then the oven's defrost setting turns the power off for a few seconds, giving
that heat time to be absorbed into the surrounding food. That heat melts a
bit more of the ice, so when the oven cycles back on, there will be more water
available to heat. Then the oven cycles off again, and the heat is again
absorbed by the surrounding ice.
If the oven did not cycle on and off, all the heat would be concentrated in
the food near the liquid water. That part would burn before the rest of the
food began to thaw.
The same is true for the other power settings of most microwave ovens.
Setting the power at 50% does not turn down the amount off microwave radiation.
Instead, the oven cycles on and off to give you about 50% of the heating that
you would get if it were on continuously.
Well, I hear a glass of eggnog calling, so I will again wish you a very happy
New Year and sign off for now.
Have a wonder filled week!
All lessons are brought to you by The Teacher's Corner and Robert Krampf's Science Education Company.
Robert Krampf's Science Shows www.krampf.com
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