Infrared Radiation: Heat Transferred through Space
Electromagnetic radiation is energy transferred by electromagnetic waves (waves consisting of oscillating electric and magnetic fields moving at the speed of light). Solar energy is electromagnetic radiation. All of the electromagnetic waves making up electromagnetic radiation are called the electromagnetic spectrum; infrared radiation and visible light are part of this spectrum.
In this project, you will determine the effect of color on the absorption and emission of infrared radiation in solar energy. You will discover how the surface area of an object affects how much infrared radiation it will absorb. You will also compare infrared radiation from space to infrared radiation from Earth's surface.
Purpose: To determine the effect of color on the absorption of infrared radiation.
- two 4-by-4-inch (10-by-10-cm) squares of construction paper, 1 black, 1 white
- 2 thermometers
- transparent tape
- 6-by-12-inch (15-by-30-cm) piece of heavy cardboard or a board of comparable size (size is not critical)
- walnut-size piece of clay
- Make a paper cover for one of the thermometers by wrapping a single layer of the black paper around the thermometer's bulb, folding the bottom edge over the end of the thermometer. Secure the paper with tape. You have a prepared a black paper-thermometer system.
- Repeat step 1, using the white paper and the second thermometer. You have prepared a white paper-thermometer system.
- Record the thermometer reading on each thermometer as the starting temperatures in a Paper-Thermometer Systems Data table like Table 23.1.
- Lay the paper-thermometer systems side by side on the cardboard and secure them with tape.
- Use the clay to stand the pencil vertically at one end of the cardboard.
- Take the cardboard outside on a sunny day and place it on the ground. The surface of each packet on the cardboard should be at a 900 angle to the Sun's rays. To obtain this angle, use dirt to elevate the end of the cardboard where the pencil stands so that the pencil casts no shadow, or the shadow is only a small area around the base of the pencil. Adjust the cardboard periodically during the experiment to keep its surface at or near a 900 angle to the Sun's rays.
- Every minute for a total of 5 minutes, read the temperature on each thermometer and record it in the table. Then, every 10 minutes for 60 minutes, read the temperature on each thermometer and record it in the data table.
The temperature of the black paper-thermometer system changes faster. In time, the temperatures of both systems stop changing, with the black one at a higher temperature.
A wave is a periodic disturbance in a medium (substance through which something acts) or space (region without a medium). Waves transfer energy from one place to another. Electromagnetic radiation is energy transferred by electromagnetic waves; it can travel through space. Electromagnetic waves are transverse waves moving at the speed of light and consisting of rapidly alternating electric and magnetic fields at right angles to each other and to the direction in which the waves are traveling. (Transverse waves look like water waves in which the vibrations are perpendicular to the direction in which the waves are traveling.) The wavelength (distance between corresponding points of two successive waves) is shown in Figure 23.2. Electromagnetic radiation is also called radiant energy. The range of wavelengths over which electromagnetic radiation extends is called the electromagnetic spectrum. The electromagnetic spectrum, in order from short to long waves, consists of gamma rays, X rays, ultraviolet radiation, visible light, infrared radiation, microwaves, and radio waves.
Solar energy is electromagnetic radiation from the Sun containing the entire electromagnetic spectrum, including large amounts of infrared radiation (electromagnetic radiation whose wavelengths lie just beyond the red portion of visible light; also called heat waves). When infrared radiation is absorbed by an object, the object becomes hotter because its thermal energy increases. Absorption of infrared radiation by surface molecules accelerates their motion. As the movement of molecules in a material increases, the thermal energy and therefore the temperature of the material increase.
- In this investigation, infrared radiation is absorbed by the paper thermometer systems. This is evident by their increase in temperature. The only difference between the two systems is the color of the paper. The temperature of the black system rose at a much faster rate than that of the white system, indicating that the black paper was absorbing more infrared radiation than the white paper. When the systems became hotter than the surrounding air, they lost heat (transfer of thermal energy from one object to another) by conduction, convection, and radiation (the process by which hot bodies lose heat in the form of infrared radiation). In time the temperature of each system reached a thermal equilibrium, the state of a system in which the gain and loss of energy are equal. The temperature of the black system at thermal equilibrium is higher than that of the white system at thermal equilibrium because the black system has absorbed more infrared radiation from the light. Thus the black system has a high rate of energy inflow.