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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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