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Einstein Revealed
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Classroom Activity
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copy of "Seeing the Invisible" student handout (PDF
or
HTML)
- desk lamp with incandescent light bulb
- thermometer
- petri dish
- water
- two books
- infrared light
- two test tubes or glass jars
- two thermometers
- Aluminum foil
- water
Temperature, Temperature
Students should note that the change in temperature is due to the
thermometer's absorbing radiant energy from the lamp. At this point
they might identify visible light as being solely responsible for
the heating effect. When the petri dish with water is placed between
the thermometer and the lamp, the temperature will drop. Visible
light passes through water unchanged (except very deep water). A
significant amount of infrared radiation, however, is absorbed by
water. Help students notice that the visible light remains
essentially unchanged as it passes through the water in the petri
dish; therefore, water must absorb radiant energy we cannot see,
accounting for the drop in temperature.
Feel the Heat
We cannot see infrared radiation, but we can perceive it as a
sensation of warmth on our skin. Some animals are highly sensitive
to infrared radiation. Pit vipers, for example, have special sensory
"pits" that they use to locate warm-blooded prey by sensing the
infrared heat radiated by animals.
Wrap It Up
The temperature on the thermometer in the wrapped test tube should
be lower. Students should recall from the first experiment that
water absorbs infrared radiation. Aluminum foil, however, reflects
infrared radiation. Students might be familiar with "space
blankets," often given to marathon runners at the end of a race.
These blankets also reflect infrared radiation, keeping an athlete
warm by reflecting back his or her own body heat.
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