Academic journal article The Science Teacher

Clearing the Air: Using Probeware and Online Simulations to Understand the Greenhouse Effect

Academic journal article The Science Teacher

Clearing the Air: Using Probeware and Online Simulations to Understand the Greenhouse Effect

Article excerpt

This article describes a lesson on the greenhouse effect in which students explore blackbody radiation and Wien's law (Figure 1). The lesson, which has been tested in a variety of high school physics classrooms, uses probeware and online simulations and combines two well-established instructional strategies: the 5E Learning Cycle (Bybee et al. 2006) and the Prediction-Observation-Explanation (POE) demonstration (White and Gunstone 1992). This collection of activities is appropriate for either physics or Earth-space science courses.

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As demonstrated by Wagoner, Liu, and Tobin (2010), many classroom investigations intended to demonstrate the greenhouse effect do not. Most of these flawed demonstrations compare either covered and uncovered containers of air or containers of air with containers of other gases. An actual greenhouse and most classroom demonstrations of the greenhouse effect work by trapping absorbed radiative heat from a light source (e.g., the Sun) by preventing it from leaving the structure through convection. The real greenhouse effect, however, happens when so-called "greenhouse gases" in the atmosphere (e.g., water vapor, carbon dioxide, methane) absorb outgoing radiation from the Earth, regardless of the presence of convection. A greenhouse is, in fact, not a very good model for the greenhouse effect.

Rye, Rubba, and Wiesenmayer (1997) suggested it is especially important to address this difference between incoming solar radiation and outgoing terrestrial radiation in relation to greenhouse gas absorption and the greenhouse effect, a study corroborated by Henriques (2002), who recounted student misconceptions about the greenhouse effect. This article's collection of classroom activities addresses such misconceptions by having students explore blackbody radiation and Wien's displacement law. Students applying these concepts discover that the constituent gases of the troposphere respond differently to different wavelengths of radiation, and this affects the surface temperature of the Earth.

Below, the lesson is presented using the five Es: engage, explore, explain, elaborate, and evaluate. The lesson may take one or two class meetings, depending on the directions students take in the "explore" section. If needed, parts of "elaborate" could be assigned for homework. The activities align with the Next Generation Science Standards (NGSS Lead States 2013) (see box, pp. 52-53).

Engage

The lesson opens with a POE demonstration using a stack of glass plates to model the greenhouse effect (materials list, Figure 2, p. 54). The teacher should set up the demonstration about an hour ahead of time to allow the system to equilibrate, but if time is short, can use screen-grabs of probeware output at equilibration instead of live output. As shown in Figure 3 (p. 54), students observe a stack of three glass plates with a surface temperature probe atop each plate placed under a light source. The teacher projects or writes the following question on the board, along with a hand-drawn schematic for reference (numbering the plates 1 through 3, starting with the top plate):

Which plate will have the highest surface temperature? Why?

* The plate closest to the lamp (1)

* The middle plate (2)

* The plate farthest from the lamp (3)

FIGURE 1

Core concepts.

Blackbody. An idealized body that completely absorbs all radiant energy incident upon it and emits electromagnetic radiation, called "blackbody radiation," according to Planck's law.

Blackbody radiation. The radiation emitted by any object may be approximated as blackbody radiation, i.e., electromagnetic radiation that has a specific spectrum and intensity that depends only on the temperature of the object and follows Planck's law.

Greenhouse effect. The process by which outgoing terrestrial radiation is absorbed by atmospheric gases, such as carbon dioxide, methane, and water vapor, and is reradiated in all directions. …

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