Solar Cooker. soda cans, 2 straws tape, masking or duct type thermometers, 2, non-mercury type water, tap SAFETY. Name Class Date

Transcription

1 Name Class Date Inquiry Lab Solar Cooker Using Scientific Methods The sun is like a huge nuclear funace, turning hydrogen fuel into helium and releasing tremendous amounts of energy in the process. This energy reaches Earth in the form of light and heat or infrared radiation. Thoughout history, humans have used the sun s energy to make fire, heat water, grow crops, power machines, and cook food. Perform this experiment on a bright sunny day. In this investigation you will test a simple solar collecting device and use what you learn to design and build a solar cooker to heat food when exposed to energy from the sun. OBJECTIVES Experiment with a simple solar collecting device to identify factors needed to capture the sun s energy. Design and build a solar cooker to heat food samples based upon what was learned about solar collection principles. Test the solar cooker and analyze results to identify ways that the design could be improved. MATERIALS aluminum foil bags, plastic, small bowls, cereal construction paper, black and white, 2 sheets (optional) cardboard or poster board clock or watch containers, plastic, with clear lids drawing paper or note paper measuring cup mirror paint, flat finish, black plastic foam beverage cups plastic foam insulation or packing material plastic wrap scissors shoeboxes small pieces of foods, such as marshmallows, apple slices, and bell peppers soda cans, 2 straws tape, masking or duct type thermometers, 2, non-mercury type water, tap SAFETY Holt Earth Science 40 The Sun

2 Name Class Date ASK A QUESTION 1. How could an effective device be designed to use collected solar energy to cook food? FORM A HYPOTHESIS 2. Form a hypothesis that answers the question. Explain your reasoning. TEST THE HYPOTHESIS 3. Paint the outside of one of the soda cans black with flat finish paint. Allow enough time for the paint to dry completely. Leave the other can unpainted. You could also cover the outside of one can with black construction paper and the other with white construction paper if the climate is not too damp. 4. Fill the measuring cup with about 600 ml of tap water. Take an initial temperature reading of the water. Record the temperature. 5. Go outdoors with a partner. Find a sunny spot. Divide the water between the unpainted and the painted soda can. CAUTION: Edges of soda cans may be sharp. Be careful not to cut or puncture skin. Cover the cans with plastic wrap, and place them in direct sunlight. Which can do you think will heat the water to a higher temperature? Explain why you think so. 6. After 20 minutes have passed, remove the plastic wrap and slide a thermometer into each can. CAUTION: Glass thermometers are fragile and can cut or puncture skin if broken. Record the temperature. Holt Earth Science 41 The Sun

3 Name Class Date 7. Subtract the initial temperature from the new temperature readings. Which water sample reached a higher temperature? Explain why. 8. Work in groups to plan a design for a solar cooker, taking into account your hypothesis. Some things you might try are lining a bowl with foil or wrapping a piece of posterboard with foil, and shaping it into an arch or a cone, and tilting the apparatus upwards to catch the sunlight. 9. Examine the list of available materials. You can use any materials from the supply list as well as any other materials that your teacher approves. List the materials you want to use below. 10. On a separate piece of paper, draw a diagram of your plan to construct your solar cooker. 11. After you are satisfied with your design, build the solar cooker, and test it outdoors. Create a data table on a separate sheet of paper to record your temperature data and cooking times. Place the cooker in direct sunlight with a thermometer in the cooking chamber. Take an initial temperature reading and a final temperature after about 45 minutes. Record the temperature every ten minutes. 12. Revise the design if you think of improvements after the initial test. 13. Place foods, such as sliced apples or marshmallows, inside plastic bags, or use straws as skewers. Set up your solar cooker in the sun. Place the food samples inside. Time the cooking process and record your observations about your solar cooking experiment. CAUTION: Do not handle any food to which you are allergic. Do not cook any meats or meat products in your solar cooker. Do not eat any foods prepared in the lab. Holt Earth Science 42 The Sun

4 Name Class Date ANALYZE THE RESULTS 1. Explaining Methods Look at your cooker or at the design drawing you made. What is the purpose of each major part of the solar cooker you built? 2. Analyzing Methods What might make your procedures more effective? For example, if the sun s path changes during the course of the day, how would you keep the cooker properly aligned? How would you change your solar cooker to improve the design? DRAW CONCLUSIONS 3. Drawing Conclusions What is a major drawback of using solar energy to cook food? EXTENSION 1. Explaining Principles Your teacher will give you a device known as a Crookes radiometer. It was invented by William Crookes in Place the radiometer in front of a desk lamp or in direct sunlight. Describe what happens. What principle that you demonstrated with your solar cooker may help explain how the radiometer works? Holt Earth Science 43 The Sun

5 Inquiry Lab Solar Cooker Using Scientific Methods Teacher s Notes TIME REQUIRED two 45-minute class periods LAB RATINGS Teacher Prep 2 Student Set-Up 3 Concept Level 2 Clean Up 2 Easy Hard Gabrielle Schavran Syosset High School Syosset, New York SKILLS ACQUIRED Collecting Data Communicating Constructing Models Experimenting Organizing and Analyzing Data THE SCIENTIFIC METHOD In this lab students will Make Observations Ask Questions Test the Hypothesis Analyze the Results Draw Conclusions MATERIALS The suggested materials must be collected in large enough amounts to satisfy each group s design decisions. Initial tests can actually be performed with very simple materials. CAUTION: Before allowing student groups to use their solar cookers, make sure that students are not allergic to the foods being cooked. Do not allow students to cook meat or meat products in their solar cookers. Students should not eat any foods prepared in the lab. The extension activity takes very little time. You could provide one radiometer, and demonstrate it for the entire class using a desk lamp as the light source, or provide several radiometers and have groups take turns using the devices. Radiometers should be handled gently. Holt Earth Science 63 The Sun

6 TIPS AND TRICKS Divide the class into smaller groups of three to four students to work on the design problem. Allow sufficient time for groups to meet to discuss and plan their solar cookers. Some students may want to research existing designs and adapt them to the suggested materials. Ask students to think about what types of measurements they want to perform as part of this investigation as they plan their experimental procedure. Students should collect temperature data and display their results in a table or in some other graphic form. You may wish to have groups try their solar cookers at different times of the day to see if they can identify a time period when they work most efficiently. CAUTION: Remind students not to look directly at the sun or stand in a position where the sunlight is reflected directly into their eyes when setting up the solar cooker or monitoring its efficiency. Holt Earth Science 64 The Sun

7 Name Class Date Inquiry Lab Solar Cooker Using Scientific Methods The sun is like a huge nuclear funace, turning hydrogen fuel into helium and releasing tremendous amounts of energy in the process. This energy reaches Earth in the form of light and heat or infrared radiation. Thoughout history, humans have used the sun s energy to make fire, heat water, grow crops, power machines, and cook food. Perform this experiment on a bright sunny day. In this investigation you will test a simple solar collecting device and use what you learn to design and build a solar cooker to heat food when exposed to energy from the sun. OBJECTIVES Experiment with a simple solar collecting device to identify factors needed to capture the sun s energy. Design and build a solar cooker to heat food samples based upon what was learned about solar collection principles. Test the solar cooker and analyze results to identify ways that the design could be improved. MATERIALS aluminum foil bags, plastic, small bowls, cereal construction paper, black and white, 2 sheets (optional) cardboard or poster board clock or watch containers, plastic, with clear lids drawing paper or note paper measuring cup mirror paint, flat finish, black plastic foam beverage cups plastic foam insulation or packing material plastic wrap scissors shoeboxes small pieces of foods, such as marshmallows, apple slices, and bell peppers soda cans, 2 straws tape, masking or duct type thermometers, 2, non-mercury type water, tap SAFETY Holt Earth Science The Sun

8 Name Class Date ASK A QUESTION 1. How could an effective device be designed to use collected solar energy to cook food? FORM A HYPOTHESIS 2. Form a hypothesis that answers the question. Explain your reasoning. Answers may vary. Students should suggest that solar cookers could be designed using reflective materials to direct solar radiation and using the absorbant qualities of dark surfaces for heating purposes. TEST THE HYPOTHESIS 3. Paint the outside of one of the soda cans black with flat finish paint. Allow enough time for the paint to dry completely. Leave the other can unpainted. You could also cover the outside of one can with black construction paper and the other with white construction paper if the climate is not too damp. 4. Fill the measuring cup with about 600 ml of tap water. Take an initial temperature reading of the water. Record the temperature. Answers may vary. 5. Go outdoors with a partner. Find a sunny spot. Divide the water between the unpainted and the painted soda can. CAUTION: Edges of soda cans may be sharp. Be careful not to cut or puncture skin. Cover the cans with plastic wrap, and place them in direct sunlight. Which can do you think will heat the water to a higher temperature? Explain why you think so. Answers may vary. Some students may anticipate that a shiny surface, or one covered with white construction paper, reflects sunlight and a black surface absorbs more heat. 6. After 20 minutes have passed, remove the plastic wrap and slide a thermometer into each can. CAUTION: Glass thermometers are fragile and can cut or puncture skin if broken. Record the temperature. Answers may vary. Holt Earth Science The Sun

9 Name Class Date 7. Subtract the initial temperature from the new temperature readings. Which water sample reached a higher temperature? Explain why. Answers may vary. The water in the black soda can should be several degrees warmer than the water in the unpainted soda can. The shiny or white can reflects both light and heat away from the water, while the dark painted surface absorbs more infrared radiation. 8. Work in groups to plan a design for a solar cooker, taking into account your hypothesis. Some things you might try are lining a bowl with foil or wrapping a piece of posterboard with foil, and shaping it into an arch or a cone, and tilting the apparatus upwards to catch the sunlight. 9. Examine the list of available materials. You can use any materials from the supply list as well as any other materials that your teacher approves. List the materials you want to use below. Answers may vary. 10. On a separate piece of paper, draw a diagram of your plan to construct your solar cooker. 11. After you are satisfied with your design, build the solar cooker, and test it outdoors. Create a data table on a separate sheet of paper to record your temperature data and cooking times. Place the cooker in direct sunlight with a thermometer in the cooking chamber. Take an initial temperature reading and a final temperature after about 45 minutes. Record the temperature every ten minutes. 12. Revise the design if you think of improvements after the initial test. 13. Place foods, such as sliced apples or marshmallows, inside plastic bags, or use straws as skewers. Set up your solar cooker in the sun. Place the food samples inside. Time the cooking process and record your observations about your solar cooking experiment. CAUTION: Do not handle any food to which you are allergic. Do not cook any meats or meat products in your solar cooker. Do not eat any foods prepared in the lab. Holt Earth Science The Sun

10 Name Class Date ANALYZE THE RESULTS 1. Explaining Methods Look at your cooker or at the design drawing you made. What is the purpose of each major part of the solar cooker you built? Answers may vary. Student designs probably used black paint or black construction paper to absorb heat, reflective materials such as aluminum foil or mirrors to direct the sun s rays, plastic wrap, bags, or plastic foam to act as insulation, or they may have used special methods of gathering or focusing the sun s energy. 2. Analyzing Methods What might make your procedures more effective? For example, if the sun s path changes during the course of the day, how would you keep the cooker properly aligned? How would you change your solar cooker to improve the design? Answers may vary. It may be necessary to move the cooker or change the angle at which it is tilted to catch the sun s rays. DRAW CONCLUSIONS 3. Drawing Conclusions What is a major drawback of using solar energy to cook food? Answers may vary. Generally speaking, passive solar systems will not work when the sun is not shining. You need to find a way to store the energy so that it can be used at times when clouds or other weather conditions interfere with solar collection. EXTENSION 1. Explaining Principles Your teacher will give you a device known as a Crookes radiometer. It was invented by William Crookes in Place the radiometer in front of a desk lamp or in direct sunlight. Describe what happens. What principle that you demonstrated with your solar cooker may help explain how the radiometer works? Answers may vary. The vanes begin to spin rapidly in direct light. One side of each vane is silvered and the other is colored black. The black side is warmer because it absorbs light energy and the silvered side, which reflects light would be cooler. The temperature difference is converted into mechanical energy causing the vanes to turn. Holt Earth Science The Sun