Heat Transfer - Radiation and the Greenhouse Effect
Objective
Big Idea
Getting Started
In this lab students explore a model of heating of Earth's surface by solar radiation with and without an atmosphere. It is meant to help them explore heart transfer by radiation, albedo, greenhouse effect and uneven heating of Earth's surface.
The set up for the lab is easy but time management is critical as students must collect 30 minutes of data in one session, a difficult task for some.
You will need one set of of the following materials for each group of 3-4 students.
- (1) Clamp lamp with aluminium reflector and heat lamp
- (4) Containers with lids or plastic wrap (pint size plastic containers w/ lids or work well)
- Potting soil/sand mixture (75/25); about 2 cups per group
- tap water
- (4) thermometers
- timers (1 per group)
Elicit
I start this lesson by asking students to think about how the surface of the Earth is heated by the sun. "How does heat from the sun warm the Earth?"
Some, but not all, usually know a bit about electromagnetic radiation. I like to use this time to discuss a little about EM radiation and introduce the idea of heat transfer by the EM waves.
If you should need a refresher in EM spectrum here is nice summary from Bozeman Science
Explore
Key questions:
- Do different earth materials heat up and cool down at the same rate?
- What effect does the atmosphere have on the rate of heating and cooling of land versus water?
Materials
- 2 containers of Sand/Soil mix
- 2 containers of water
- 4 thermometers
- Plastic wrap or lids
- Heat lamp
- Timer
- Heat Transfer- Radiation Investigation handout
Set-Up
1. Fill each container with 150 ml of either water or sand/soil mix. You will two of each.
2. Cover one container of water and one container of mix with plastic wrap or a lid. You will need a hole in the lid to place the thermometers.
3. Place a thermometer into each container, securing it so it measures the temperature just under the surface of the substance in the container.
Data Collection
1. Record the starting temperatures on the data table.
2. Turn on the lamp and record the temperature of each substance every minute for 15 minutes.
3. At the end of fifteen minutes, turn the lamp off.
4. Continue to record temperatures for each substance every minute for fifteen minutes as they cool.
Data Analysis
When finished, students create two graphs of the data The first graph shows change in temperature over time of the water with and without a lid. Use a different symbol of color for each set of data. The second graph shows change in temperature over time of the sand/soil mix with and without a lid.
Be sure to have students include a key, label the axis and include a title. Have them use their graphs to answer the follow up questions.
- Which materials absorbed more heat in the first 15 minutes?
- Which materials lost the most heat in the last 15 minutes?
- Imagine that it’s summer and that the sun is shining on the ocean and on a stretch of land. Which will heat up more during the day? Which will cool more slowly at night? Explain.
- How do you think the surface of the materials heated up?
- How do you think the materials below the surfaces heated up?
- What properties of the earth may have caused them to heat and cool at different rates?
- How would the uneven energy absorption by different surfaces on earth (water, soil, snow, trees, etc.) affect the atmosphere?
If your students have not plotted data sets before, use the time to help them set up the graphs and model for them how to do this. This is valuable skill that they will use many more times in future lesson.
Explain
This lesson will most likely run two days if students graph the data and complete the follow up questions in class. If time is a concern, those parts could be assigned for homework and then discussed.
I make sure during the discussion to bring the class ideas back to heat transfer and radiation. I found it necessary to revisit why we took measurement of temperature at or just below the surface of the material and not at the bottom of the container. You want students to understand that how heat energy is first transferred by means of radiation at the surface and then by way of conduction to the soil below. This helps to connect these two forms of heat transfer.
You could expand this to a more in depth investigation of greenhouse effects, albedo or other related phenomena.
