Teacher's Notes
Objective:
Students gain an understanding that dark colored objects absorb energy faster than light colored objects.
Background:
While solar energy can be used immediately to warm a house, it is often stored as heat to be released slowly into an area to be heated. Solar collectors are usually dark, as dark colors absorb heat more rapidly than light objects. Water is often heated by solar energy and used to store the energy. Water warms
slowly, but holds its heat and cools slowly. This allows the slow release of stored solar energy. In this activity students not only determine the fastest absorbers of solar energy, but the slowest releasers of solar energy.
Materials:
Lamp with 150 watt bulb, or sun lamp
Bottom 3 cm of 5 styrofoam cups
Light colored sand
Dark colored dirt
Thermometers
1 sheet graph paper (coordinate paper)
Teaching Suggestions:
1. Caution students to handle the thermometers with care. Use alcohol thermometers for this activity as they present less of a hazard if broken than mercury thermometers.
2. This activity could be done outside on a sunny day when the sun is high in the sky. The procedure is the same as far as recording temperatures for 5 minutes and then remove the cups from the sun. Record the cooling rates of each cup as in the listed procedure.
Extended Activities:
Have students relate any experiences of their own to support the difference in absorption of solar energy. Examples might be walking on hot sand to get to cool water, or dark clothes get warm in the sun, while light colored clothes don't seem to get as warm.
Introduction:
One of the most interesting things about the transfer of energy by radiation is how the characteristics of the material which is absorbing the energy affects the amount of energy transferred. In this activity we will compare the ability of different substances to absorb and lose energy to change temperature.
Materials:
Lamp with 150 watt bulb, or sunlamp
Bottom 3 cm of 5 styrofoam cups
Light colored sand
Dark colored dirt
Thermometers
graph paper
Follow These Procedures:
Part A: Determine the change in temperature from the absorption of radiant energy in five different substances:
Water
Dry light sand
Wet light sand
Dry dark dirt
Wet dark dirt
1. Use five cups, one with each of the materials listed above.
2. Arrange the cups in as small a circle as possible without having them touch each other.
3. Place a thermometer in each cup so the bulb is 0.5 cm below the surface of the material. (You will need to hold or clamp the thermometer in that position in the water.)
4. Place a lamp 20 cm above the containers and directly over the center of the circle.
5. Read and record the temperature of each material just before turning on the lamp. Turn on the lamp and record the temperature at regular intervals of one
minute for 5 minutes. Then turn off the lamp and continue to record the temperature at regular intervals of one minute for 5 more minutes. Record your results in a table. Think about what you will measure and design a good table in which to record your results.
Part B: Graph the data from the investigation. Label the lines showing the temperatures of the five different materials.
Answer These Questions:
1. During the five minutes the light was on, where did the energy come from to change the temperature of the substances in the cups?
How was this energy transferred to the cups?
2. Of the two wet solids, which warmed the fastest?
If the two wet solids have the same heat capacity, the one that warmed more must have absorbed more energy. What characteristic caused it to absorb more radiant energy?
3. Which two materials warmed the fastest?
Explain why they warmed up more rapidly than the other materials.
4. Where did the heat energy go when the materials cooled?
How long was the energy transferred away from the cups during the cooling?
5. Which material cooled off most rapidly after the light was turned off?
Explain why it cooled most rapidly.
Teacher's Pages
Objective:
Students estimate wind speed by observing the wind's effect on lake or pond surfaces or on flexible objects such as trees, flags, and rising smoke plumes.
Background:
Wind speed can be estimated by observing the wind's effect on lake or ocean surfaces or on flexible objects such as trees. Such observations are the basis
of the Beaufort scale, which is a graduated sequence of wind strength. These graduations range from 0 for calm conditions to 12 for hurricane strength winds. The scale carries the name of Sir Francis Beaufort, who developed the scale in the early 1800s. Beaufort served as a ship's commander in the British Navy.
His goal was to standardize terms used by sailors in describing the state of the sea under various wind conditions. In 1838, after some revision, the British Navy adopted the Beaufort scale. In 1853 the scale was sanctioned for
international use by sailors. Later, when the scale was extended from sea to land, it was necessary to develop wind speed equivalents for each Beaufort number. This development was done in 1926. The Beaufort scale is still in use today.
Materials:
No materials needed
Teaching Suggestions:
1. Have students practice using the Beaufort Scale individually. Then have the students compare their results. Try to arrive at a consensus on the wind speeds at various times during the school day.
2. If students have already made the Ping-Pong ball-protractor wind speed measurer, have them compare their Beaufort estimates to measurement obtained with the wind speed tool.
3. Your students and you might wish to convert the Beaufort scale to wind speeds in miles per hour rather that using km/hr. To do this remember that 1 kilometer = 0.61 mile. Therefore 50 km/hr = 30.50 miles per hour.
Extended Activities:
1. Students can research the Beaufort Scale and its development. You do not have to give them the background material provided above.
2. Some libraries have Almanacs of Weather. Students can research information about wind such as the windiest places on earth, the strongest wind gust ever recorded, etc.
Problem:
At what time of day is there enough wind to make electricity where you live?
Background Information:
This is the Beaufort wind scale. It is used to measure wind speeds. It relies on human observations, not mechanical devices, to estimate the speed of the wind. It gives the Beaufort Number, the description of the wind speed, and the observation of the wind.
0 -- calm (0-1 mph) -- smoke rises vertically
1 -- light air (2-3 mph) -- smoke drifts slowly
2 -- slight breeze (4-7 mph) -- leaves rustle; wind vane moves
3 -- gentle breeze (8-12 mph) -- twigs move; flags extended
4 -- moderate breeze (13-18 mph) -- branches move; dust and paper rise
5 -- fresh breeze (19-24 mph) -- small trees sway
6 -- strong breeze (25-31 mph) -- large branches sway; wires whistle
7 -- moderate gale (32-38 mph) -- trees in motion; walking difficult
8 -- fresh gale (39-46 mph) -- twigs break off trees
9 -- strong gale (47-54 mph) -- branches break; roofs damaged
10 -- whole gale (55-63 mph) -- trees snap; damage evident
11 -- storm (64-72 mph) -- widespread damage
12 -- hurricane (73-82 mph) -- extreme damage
Activity:
1. Measure the wind using the above scale. Measure it on three different days at three different times during the day, preferably in the morning, midday, and afternoon or evening. Record your observations.
2. At what time of day do the fastest winds usually occur? the slowest winds?
3. Any wind over 8 mph can be used to generate electricity. Currently, though, it only makes economic sense to build wind turbines in areas where the wind exceeds 15 mph most of the time. Could you generate electricity in your area?
Teacher Notes
Objective:
1. Students will use thermometers to measure temperature of sunlight in direct sunlight, focused sunlight, and shadow.
2. Students will construct a line graph of the data collected.
Background:
CAUTION: If the temperature recorded by thermometer A reaches 105 degrees C, remove from the sunlight.
CAUTION: Tell the students not to use the lenses to burn holes in paper or start paper on fire.
The last section of the student text material discusses concentrating solar collectors. The illustrations in the text shows reflective materials used to make concentrating collectors. This activity uses a lens rather than a reflector. The results are the same -- concentrating sunlight can produce significant increases in temperature.
Materials:
1. Double convex lens (small hand lens about 5 cm in diameter)
2. Three Celsius thermometers (Fahrenheit thermometers are OK)
3. Graph paper
4. Rulers
Teaching Suggestions:
1. Make sure that students understand the tables before starting to collect data. Go over what .5 min. means in time
(.5 min. = 1/2 min. = 30 seconds).
2. Have students do #'s 1 - 4 on Procedure.
3. Go over how to make a line graph.
4. Have students complete Think It Over.
Extended Activities:
1. Use filters such as cellophane paper to see the effects of filtering.
2. Place thermometers in liquid and measure temperature changes of focused sunlight and shadow.
Problem:
What are some effects of concentrating sunlight?
Materials:
1. Double convex lens (5 cm or more in diameter)
2. Three Celsius or Fahrenheit thermometers
3. Graph paper
4. Rulers
Follow This Procedure:
1. Examine Table 1 and make sure you understand where you will be recording your data. Read this procedure before doing the activity.
2. Work either outdoors or at a window through which the sun shines. Label the thermometers "A", "B",and "C".
3. Read each thermometer in the shade. Record the starting temperatures in Table 1. Place thermometer B so that the bulb is in the shade -- possibly the shadow cast by your arm. Place thermometer C in direct sunlight. Then use the lens to bring sunlight to a sharp focus on thermometer A.
4. Read each thermometer every 30 seconds for 5 minutes and record their temperatures in the table.
Think It Over:
1. Make a line graph of your data. Plot time on the horizontal axis and temperature on the vertical axis. Use a dotted line for normal sunlight temperatures, a dashed line for focused sunlight temperatures, and a solid line for shadow area temperatures.
2. Compare the changes in temperature for normal sunlight, focused sunlight, and shadow. State possible reasons for the difference you notice.
3. Describe another way you could concentrate sunlight in one area.
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