Properties of Solar Radiation: Reflection, Transmission and Absorption

Overview

Students will make a solar panel. They will use it as a radiation meter to distinguish how well various materials reflect or transmit solar radiation. Students will predict reflection and transmission properties for various materials and test their predictions using their sense of touch.

Standards Addressed

Grade 9, Physical Science

09-10 Benchmark
G. Demonstrate that waves (e.g., sound, seismic, water and light) have energy and waves can transfer energy when they interact with matter.

Y2003.CSC.S03.G09-10.BG.L09.I18 / Nature of Energy

18. Demonstrate that electromagnetic radiation is a form of energy. Recognize that light acts as a wave. Show that visible light is a part of the electromagnetic spectrum (e.g., radiowaves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays).

 

Y2003.CSC.S03.G09-10.BG.L09.I19 / Nature of Energy

19. Show how the properties of a wave depend on the properties of the medium through which it travels. Recognize that electromagnetic waves can be propagated without a medium.

Materials

(one each per group of three or four students)

• 1-V, 400 mA mini–solar panel with alligator clip leads

• 45-degree mount for the solar panel

• Digital ammeter

• A flat black board such as a clipboard

• Masking tape (30 cm per group)

• If working without the sun, 150-watt incandescent bulb with lamp

• Squares of materials, approximately 10 x 20 cm

• Mirror

• Window glass

• Frosted glass

• Aluminum foil

• Wood

• Waxed paper

• Clear plastic wrap

• Cellophane: clear, yellow, red, blue, green

• Construction paper: black, yellow, red, blue, green

Procedure

1. Have students complete the Formative Assessment.

2. Divide the students into groups of three or four and have one person in each group collect the materials needed to create a solar testing device.

3. Have each group prepare one 45-degree solar panel mount as described in the Transmission, Reflection and Absorption student handout.

4. Discuss the mathematical relationship between reflection, transmission and absorption. Incident solar radiation is the amount of solar radiation striking a surface per unit of time and area. Incident solar radiation (I) must equal reflected (R) plus transmitted (T) plus absorbed (A) radiation.

I = R + T + A

5. Demonstrate how to use an ammeter and a panel’s conversion curve to obtain milliamps and then convert to watts per square meter (W/m²). If time for the activity is limited, groups can run either the transmission or reflection lab (as described further in this plan) and then share their data prior to predicting the absorption capacities of the materials.

6. If weather conditions are unsuitable, or a proper sunlit space is not available for students to work with radiation directly obtained from the sun, a 150-watt incandescent lamp can serve as an alternative. Keep any lamp at least 120 cm away from the solar panel, or it might melt the protective cover.

7. Have the students work through the handout. This may require several class sessions.

8. Have the students complete the Summative Assessment. A percentage of the number correct could be used for evaluation.

Formative Assessment Answers

1. Radiowaves should have the lowest energy and gamma rays should have the highest.

2. Students can talk about how constant X-rays can be bad, sitting out in the sun can be harmful and small amounts of gamma radiation are deadly.

Lab Answers

Results will vary due to several variables, especially variations in light conditions and the positioning and holding of the solar cell.

The mirror and aluminum foil should show the highest levels of reflection. Window glass and clear plastic sheeting should show the highest level of transmission. The mirror, aluminum foil, copper sheeting, wood and construction paper should not transmit light energy.

Summative Assessment Answers

1. Reasoning for predictions will vary.

2. Thick and scratchy materials absorb more light.

3. The darker colors absorb more light.

4. Panels should be made all the same. Time during experiments should be about the same.

5. Light exterior and interior car colors in a sunny environment would reflect light. The opposite is true in a cold, sunny climate.

6. You would want the highest transmission so the light can pass through the cover and hit the solar panel. The description of the material should resemble window glass and clear plastic sheeting.

*adapted from Solar Ed for NY School Power