LAB - Absorption and Radiation of Energy. Introduction: Earth's surface varies in
both chemical and physical properties. The wavelength of solar radiation that is ...
Name: __________________________________ LAB - Absorption and Radiation of Energy Introduction: Earth’s surface varies in both chemical and physical properties. The wavelength of solar radiation that is absorbed by an earth material is changed and re-radiated as heat. The characteristics of a surface determine what happens to the incoming solar radiation. The temperature range of outer space and on planetary bodies is affected by a wide range of factors. In outer space, the temperature on a surface depends upon whether that surface is in sunlight and if so, the angle of that surface to the Sun's rays. On a planetary body, the temperature also varies with the ambient atmospheric temperature, winds, and nearby surface materials .For example, on Earth temperatures can vary dramatically on a summer day between asphalt parking lots and grassy borders. Objective: You will determine how the surface characteristics of a material affect the relative rates of energy absorption and radiation. Hypothesis: Write a statement about which can you think will heat and/or cool faster and why.
Vocabulary: Absorption:
Reflection:
Re-radiation:
Radiative Balance:
Procedure:
YOU MUST WEAR SAFETY GOGGLES!
1.
Arrange the black and shiny (white) cans as shown in the diagram.
2.
On the Report Sheet, record the temperature of each thermometer at Time 0.
3.
Turn on the lamp and read the thermometers every minute for 10 minutes. Record these data on the Report Sheet.
4.
Without touching or moving the cans, turn off the lamp and turn the lamp away from the cans. CONTINUE TIMING.
5.
Continue to take temperature readings every minute for another 10 minutes (20 minutes total) recording the data on your Report Sheet.
6.
Graph your data. Plot both curves on the same set of axes. Place time on the horizontal axis. Be sure to label each line.
Discussion Questions: 1. Why was it important to place each can an equal distance from the lamp?
2.
After 10 minutes, why was it necessary to turn the lamp away from the cans?
3.
Which can absorbed energy more quickly? How does your graph show this?
4.
Which can reradiated energy more quickly? How does your graph show this?
5.
Which can had the greatest rate of change throughout this experiment?
6.
What evidence can you find from your graph that neither can heated nor cooled at a constant rate?
7.
If a surface is a good absorber of energy, what can you infer about its ability to radiate energy?
8.
What would cause the graph lines to tend to level off near the end of 20 minutes?
9.
How do the wavelengths absorbed by the cans differ from the wavelengths radiated by the cans?
Conclusion: What characteristic of the surface used in this lab determined the rates of heating and cooling and how did this compare to your hypothesis?
Reading Comprehension Read the portion of the article on Cooling Cities below and answer the following questions based on the reading. Use complete sentences.
White Heat Cooling cities one roof at a time By Juliane Poirier
http://www.bohemian.com/bohemian/09.07.11/greenzone-1136.html
For climate and life protection, dress roofs in white. Seven hundred heat-related deaths in the 1995 Chicago heat wave may have been prevented by white-roofed buildings, according to physicists at Lawrence Berkeley National Laboratory. Famous among these scientists is Art Rosenfeld, who helped present the winning statistics now persuading cities all over the world to require light roofing materials in building codes. Rosenfeld explained to a Berkeley audience last fall that dark materials absorb and hold heat, and that a nonreflective roof captures heat and transfers it to the entire building, increasing temperatures up to 50 degrees (!). Of the 737 Chicago heat-wave deaths, 700 were residents of upper floors in buildings with no air conditioning and dark roofs. Climate scientists have long known that light-colored surfaces bounce sunlight back and dark surfaces trap light and store heat, forcing temperatures up. But Rosenfeld observed that this fact was not altering roofing codes; so he and others calculated dark-surface damages in terms of C02 rather than temperature, and got the world's attention. "Carbon dioxide [not temperature] has a price on the market," Rosenfeld explained. Last year, it was about
$250 per ton. "So we calculated that an average-sized house contributes 10 tons of C02 per year. Multiply by about 3 billion, because there are about that many roofs, and [by making roofs reflective] you would avoid the heating effect of 25 billion tons of C02. That's over the life of the roof—about 20 years. It would be the equivalent of turning off the entire world for a month or taking 300 million cars off the road for 20 years." In 2005, California's Title 24 building codes required that modified flat roofs be white, and in 2008 updated codes required the same for all sloped residential roofs visible from the street in the five hottest zones (the state has 16 "building climate zones"). The codes in 2012 are expected to be even tighter. (Opponents to white-roof codes might be consoled by the fact that light colored roofs and roads last longer and are costsaving in addition to cooling.) So far only Arizona, Georgia and Florida have followed California's lead. But through an organization spearheaded by Rosenfeld and his colleagues, the world's urban centers elsewhere around the globe (all urban roofs, collectively, would cover an area the size of California) have taken action via www.whiteroofalliance.com. Actions to take at home include lightening roofs and paved surfaces, and planting trees.
1. What do dark materials do with heat?
2. How many tons of C02 does an average sized house contribute?
3. Why would someone in New York State want a dark colored roof?
