Infrared Radiation: Heat Transferred through Space (page 2)

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Author: Janice VanCleave

Try New Approaches

  1. How does the surface area of a material affect the amount of radiation that it absorbs? Repeat the investigation, turning the paper packets so that their narrow edges are facing the Sun.
  2. Does the color of the systems affect the rate at which they emit radiation? Design a way to cool the systems. One way would be to place each system in a plastic, resealable bag and lay the bags in an ice chest.

Design Your Own Experiment

    1. How does the heat radiating from space compare with that radiating from Earth's surface? Design a way to measure radiation from a specific direction. One way is to make a heat telescope to capture the radiation. A heat telescope could be made by placing a thermometer inside an aluminum foil cone. Two heat telescopes, one pointed at the sky and the other toward Earth, could be used to compare the radiation from the two directions. Each telescope could be made using a 12-by-18-inch (30-by-45-cm) piece of heavy-duty aluminum foil. Place the shorter sides of the foil piece together and fold over the ends several times to form a cylinder. Insert the bulb end of the thermometer into the narrow end of the aluminum foil cylinder. Squeeze the foil around the thermometer, forming a funnel shape. Adjust the position of the thermometer so that the bulb is just above the bottom of the foil cylinder. Allow the two heat telescopes to remain side by side on a table for 2 or more minutes until they register the same temperature. Record this temperature as the initial temperature, Tl, for both thermometers. On a clear day, take the two heat telescopes outdoors. At the same time, point one heat telescope toward the sky and the other toward the ground. After 1 or more minutes, read and record the temperature readings of each heat telescope, as the final temperature, Tf. Repeat the experiment four or more times. Calculate the change in temperature due to radiation from space (ΔTs) by determining the absolute difference between Ti and Tf for the heat telescope pointed toward the sky. Calculate the change in temperature due to the radiation from Earth's surface (ΔTe) by determining the absolute difference between Ti and Tf for the heat telescope pointed toward the ground. Average the results for each telescope.
    2. Calculate a space-to-Earth radiation ratio using this equation:
    3. Is the space/Earth radiation ratio the same at night? Repeat the previous investigation at night.

    4. What effect, if any, do barriers such as trees have on radiation from space? Is there more radiation coming from one direction of the sky than from another? Do different surfaces on Earth affect how much radiation comes from Earth? Design ways to answer these questions using the heat telescope.

Get the Facts

  1. An object's ability to absorb and emit radiation is called its emissivity. A perfect blackbody or, simply, a blackbody has an emissivity of 1. What is a blackbody, and how does its emissivity compare to that of other objects? For information, see Louis A Bloomfield, How Things Work: The Physics of Everyday Life (New York: Wiley, 1997), p. 268.
  2. Solar radiation consists mainly of visible light, ultraviolet radiation, and infrared radiation. How do these forms of radiation differ? For information, see Mary and Geoff Jones, Physics (New York: Cambridge University Press, 1997), pp.116-117.
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