Introduction
In this lab, students investigate how different materials transfer heat by testing substances such as sand, soil, clay, and gravel. By comparing results, they will see that materials vary widely in their ability to conduct heat, and that water content and density play important roles. This activity helps students connect their observations to real-world applications in geothermal energy, where engineers must understand how underground materials affect heat flow.
Student Objectives
Students will be able to
- Measure and record temperature changes in different materials as they are heated.
- Compare how sand, soil, clay, and gravel transfer heat under the same conditions.
- Explain how material properties such as density and water content affect heat transfer.
- Connect their experimental results to real-world applications in geothermal energy and energy system design.
Materials
(per group)
- Student Handout
- Metal tray or glass beaker that can be heated to hold test material
- One test material (examples below); 5 cm thick layer in designated tray or beaker
- Dry sand
- Moist sand
- Dry soil
- Moist soil
- Clay
- Small stone gravel
- Hot plate (low setting)
- Insulating mat (cork mat or silicone pad)
- 2 thermometers (digital probes preferred)
- Safety glasses, heat-resistant gloves and/or beaker tongs
- Ruler
Procedure
- Preparation Before the Lab
- Run a trial run before class to gauge heating times with your equipment.
Check hot plate type: If dial-based, determine the right setting on the dial to keep the temperature around 50 degrees Celsius for this experiment (window of 40 – 60 degrees). If digital, set the target surface temperature to 50 degrees Celsius. - Ensure trays or beakers fit securely on the hot plate surface, and have heat-resistant gloves and tongs available. Demonstrate safety procedures before students begin the experiment.
- Run a trial run before class to gauge heating times with your equipment.
- During the Lab
- Each student group will be assigned a material to test using the instructions on the Student Handout to safely conduct the experiment. Note: Students will not be touching the trays or hot plate surfaces once the heating begins. They will only handle the thermometers.
- Give students specific instructions on what setting to put their hot plates on, based on the pre-lab preparation conclusions.
- After the Lab
- Turn off hot plates and allow containers to cool before disposal and clean up.
- Provide a location on the board or poster paper where groups can report the rate of heat transfer (this calculation is part of the graphing section of the Student Handout). Students will use this whole-class data to answer the analysis questions.
Assessment Rubric
| Category | Exceeds Expectations | Meets Expectations | Needs Improvement |
|---|---|---|---|
| Safety and Procedures | Consistently follows all safety rules and sets up/uses equipment correctly without reminders. | Follows most safety rules and sets up/uses equipment mostly correctly; may need an occasional reminder. | Often forgets safety rules or sets up equipment incorrectly; unsafe or unreliable procedure. |
| Data Collection and Organization | The data table is complete, accurate, and neatly organized at all time intervals. | Most data has been collected correctly; the data table is mostly clear and organized. | Many missing/inaccurate data points; the data table is incomplete/ disorganized. |
| Analysis and Interpretation | Clearly explains Probe A vs. Probe B trends with correct reasoning; graphs are accurate and labeled. | Describes trends with some correct reasoning; graphs may have minor errors. | Little or incorrect explanation of trends; incomplete or missing analysis. |
| Hypothesis and Conclusion | Hypothesis is clear and based on material properties. Conclusion strongly supported by data, with discussion of errors/improvements. | Hypothesis reasonable; conclusion somewhat supported by data; limited reflection on errors. | Hypothesis vague or missing; conclusion unsupported or absent. |
| Connections and Engagement | Actively participates and makes strong, thoughtful connections to real-world geothermal applications. | Participates and makes basic or general real-world connections. | Rarely participates; no or inaccurate real-world connections. |
Answer Key
The Student Guide contains the Geothermal Conductivity Lab – Student questions.
Analysis and Conclusion Questions
- Answers will vary.
- Answers will vary. (Example: Materials with higher density and more tightly packed particles usually conduct heat better. Moisture also increases conductivity because water transfers heat more effectively than air. On the other hand, dry or porous materials conduct heat more slowly. Composition matters too. For example, minerals like quartz or granite conduct heat better than organic-rich soils.)
- Answers will vary. (Sample response: Our material (moist soil) showed a moderate rate of heat transfer compared to others. It heated faster than dry sand and clay, but slower than gravel.)
- Answers will vary. (Sample response: Yes, my hypothesis was supported. I predicted that moist soil would conduct heat better than dry soil because of the water content.)
- Answers will vary. (Example: Possible errors include inconsistent probe placement, small variations in layer thickness, delays in recording the time, or slight differences in packing the material. Repeating the experiment several times would reduce random errors and give a more reliable average, making our conclusions more confident.)
- Answers will vary. (Example: Engineers need this information to know how quickly heat can flow toward wells or pipes. If conductivity is too low, the system may overcool the reservoir or underperform. With accurate data, engineers can design systems that extract heat efficiently long-term.)
- Answers will vary. (Example: If the rock has low conductivity, heat will not move fast enough to replace the heat being removed. This could cause the reservoir to cool too quickly, reduce the efficiency of electricity generation, and possibly make the plant unsustainable in the long-term.)
- Answers will vary depending on the material tested. (Sample response: Since our material showed high thermal conductivity, engineers could design the system to extract heat at a faster rate without cooling the reservoir too quickly. For long-term efficiency, they might use the site for electricity generation, since high-conductivity rock can provide a steady, reliable flow of heat.)
- The granite site would be better for electricity generation, because it allows a steady, strong flow of heat to the wells. Clay, with low conductivity, would heat up slowly and not provide enough energy for efficient electricity generation.)
- Answers will vary. (Example: Iceland likely has underground materials with high conductivity and active volcanic systems, so heat moves quickly to the surface and provides a strong energy supply. In regions with low-conductivity materials underground, the heat does not travel as efficiently, making geothermal energy less effective and only useful for smaller-scale direct heating.)