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Science Experiment on Heat Radiation

Radiation is the process of electromagnetic waves traveling though space at the speed of light. It is a method of heat transportation that does not require contact with a source for an object to heat. The sun is a primary example of this. Electromagnetic waves carrying warmth from the sun travel through space to heat the earth. You do not have to touch the sun to feel its warmth. A science experiment on heat radiation can help students understand how heat from the sun is transferred to an object and how the color of that object affects how heat radiation is absorbed and emitted.

Materials
- For this experiment, you will need to gather black and white construction paper, heavy cardboard, two thermometers, scissors, transparent tape, a pencil, a watch and a piece of clay the size of a walnut. Cut two 4-by-4-inch squares out of both the black and white construction paper. The cardboard will need to be at least 6 inches wide by 12 inches long.
Method
- Wrap the bulb of one of the thermometers in a layer of black construction paper and secure it with tape. Repeat this step with the white construction paper on the second thermometer. Make sure to leave the top exposed so that you can get the temperature readings from each thermometer. Record the temperature reading on each of the thermometers as the "starting temperature" on a sheet of paper. Lay both thermometers side by side on the cardboard and secure them with tape. Make sure that the reading line is exposed so that you can record the temperature measurements. Press the clay onto the top of the cardboard and stick the pencil in it so that it stands vertically. Take the cardboard outside in the sun and lay it facing up on the ground. Use dirt to elevate the top end of the cardboard so that the pencil does not cast a shadow. You will need to adjust the cardboard elevation periodically throughout the experiment to ensure that the pencil does not cast a shadow.
Procedure
- Record the temperature readings on each thermometer every minute for the first five minutes, then every 10 minutes for the next 60 minutes. Make sure to adjust the elevation of the cardboard when the pencil begins to cast a shadow. Note how the temperature of the thermometer covered in black construction paper rises faster. At a certain point, the temperature on both thermometers will quit rising.
Results
- Heat from the sun is a form of infrared radiation. The construction paper on each of the thermometers absorbed that radiation and changed the temperature of the thermometers. The temperature of the thermometer covered in black construction paper rose much faster because it was absorbing more infrared radiation than the white construction paper. When the temperature of both thermometers became hotter than the surrounding air, they began emitting heat and the temperature of the thermometers quit rising. This is called thermal equilibrium: the state in which the gain and loss of heat are equal. The thermometer covered in black construction paper achieved thermal equilibrium at a much higher temperature because it absorbed more heat radiation than the thermometer covered in white construction paper.

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