H.S. Solar Energy: Waves and Solar Cell Technology

Transcription

1 D R I G r e e n P o w e r P r o g r a m G r e e n B o x H.S. Solar Energy: Waves and Solar Cell Technology Created by: Learning Cycle 5E Lesson Based upon and modified from Roger Bybee* (1990) *Bybee, R & Landes, N. (1990). Science for life and living: An elementary school science program from Biological Sciences Curriculum Study (BSCS). American Biology Teacher. 52 (2)

2 Waves and Solar Cell Technology Next Generation Science Standards (NGSS) Physical Science: HS-PS1-4. Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy. HS-PS2-6. Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials. HS-PS3-2. Develop and use models to illustrate that energy at the macroscopic scale can be accounted for as a combination of energy associated with the motions of particles (objects) and energy associated with the relative positions of particles (objects). HS-PS3-3. Design, build, and refine a device that works within given constraints to convert one form of energy into another form of energy. HS-PS3-5. Develop and use a model of two objects interacting through electric or magnetic fields to illustrate the forces between objects and the changes in energy of the objects due to the interaction. HS-PS4-1. Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling in various media. HS-PS4-5. Communicate technical information about how some technological devices use the principles of wave behavior and wave interactions with matter to transmit and capture information and energy. HS-PS1-5. Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs. Earth Science: HS-ESS3-4. Evaluate or refine a technological solution that reduces impacts of human activities on natural systems. Background Knowledge Teacher: The following is an excerpt from the National Research Council. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas. Washington, DC: The National Academies Press, Waves are a repeating pattern of motion that transfers energy from place to place without overall displacement of matter. Light and sound are wavelike phenomena. By understanding wave properties and the interactions of electromagnetic radiation with matter, scientists and engineers can design systems for transferring Solar Energy Green Box: Lesson 4 Waves and Solar Cell Technology 2

3 information across long distances, storing information, and investigating nature on many scales some of them far beyond direct human perception. The wavelength and frequency of a wave are related to one another by the speed of travel of the wave, which depends on the type of wave and the medium through which it is passing. The reflection, refraction, and transmission of waves at an interface between two media can be modeled on the basis of these properties. Combining waves of different frequencies can make a wide variety of patterns and thereby encode and transmit information. Information can be digitized (e.g., a picture stored as the values of an array of pixels); in this form, it can be stored reliably in computer memory and sent over long distances as a series of wave pulses. Solar cells are human-made devices that likewise capture the sun s energy and produce electrical energy. These photoelectric materials emit electrons when they absorb light of a high-enough frequency. Electromagnetic radiation (e.g., radio, microwaves, light) can be modeled as a wave pattern of changing electric and magnetic fields or, alternatively, as particles. Each model is useful for understanding aspects of the phenomenon and its interactions with matter, and quantum theory relates the two models. Electromagnetic waves can be detected over a wide range of frequencies, of which the visible spectrum of colors detectable by human eyes is just a small part. Many modern technologies are based on the manipulation of electromagnetic waves. All electromagnetic radiation travels through a vacuum at the same speed, called the speed of light. Its speed in any given medium depends on its wavelength and the properties of that medium. At the surface between two media, like any wave, light can be reflected, refracted (its path bent), or absorbed. What occurs depends on properties of the surface and the wavelength of the light. When shorter wavelength electromagnetic radiation (ultraviolet, X-rays, gamma rays) is absorbed in matter, it can ionize atoms and cause damage to living cells. However, because X-rays can travel through soft body matter for some distance but are more rapidly absorbed by denser matter, particularly bone, they are useful for medical imaging. Photovoltaic materials emit electrons when they absorb light of a high-enough frequency. This phenomenon is used in barcode scanners and electric eye systems, as well as in solar cells. It is best explained using a particle model of light. Any object emits a spectrum of electromagnetic radiation that depends on its temperature. In addition, atoms of each element emit and preferentially absorb characteristic frequencies of light. These spectral lines allow identification of the presence of the element, even in microscopic quantities or for remote objects, such as a star. Nuclear transitions that emit or absorb gamma radiation also have Solar Energy Green Box: Lesson 4 Waves and Solar Cell Technology 3

4 distinctive gamma ray wavelengths, a phenomenon that can be used to identify and trace specific radioactive isotopes. Student: A. Prior Standards: Time a. MS.Waves and Electromagnetic Radiation b. MS.Engineering Design B. Life Experience: Students have had a great deal of personal experience with waves and their applications in technology. For example, students have worked with many different types of technologies that utilize wave properties including radios, microwaves, digital cameras, X-rays, and much more. When students tune their radio, watch TV, send a text message, or pop popcorn in a microwave oven, they are using electromagnetic energy. We depend on this energy every hour of every day. Without it, the world we know could not exist minutes Materials List Include a detailed list, in bulleted list form, of materials needed for this lesson. Student Guides Wave Technology PPT One solar module per group of 2-3 One multi-meter per group of 2-3 Compact fluorescent lamp Different colored gels Incandescent lamp Flashlight Long wave UV flashlight (teachersource.com) Magnifying glass (or plastic) Mirror (or other reflective surface) Tape to mark distance in inches on wall or, 1 measuring tape per group of Long jump rope Safety Procedures Ensure there is plenty of room for the Engagement exercise so students aren t struck by the rope. Some of the light sources might get hot to the touch and others might break if not handled correctly. The UV light is never to be looked at directly. Solar Energy Green Box: Lesson 4 Waves and Solar Cell Technology 4

5 Have students work with these materials with gentle hands to ensure safety. Show students the proper way to work with those materials that may cause safety hazards. Continually monitor student work. Engagement After showing students Slide 1 & 2, have two students stand at the front of the class with a jump rope. Ask students to wave the rope very slowly. As the students make waves, show a picture of a radio on Slide 3. Ask student to go a little faster. Show the next slide, a microwave oven. Ask students to go a little faster. Show the next picture of a remote control. Have students go faster. By now students should be moving the jump rope rather quickly. Show students a picture of a light bulb (to represent visible light). Ask them to go faster again. This time Slide 7 representing UV light. Tell them to go faster yet, show the image of a PET/CT scan. Finally, have students wave the rope as fast as they can and show the image of terrestrial gamma-ray flashes. Present Slide 10. Ask students how the motion of the jump rope relates to the electromagnetic spectrum. Ask students which frequency requires more energy (in particular, ask the students moving the jump rope). Have students explain how wavelength and frequency relate. Ask students to point out what the human eye can see on the electromagnetic spectrum. Move on to Slide 11, explaining that this is the same wavelength that PV cells respond to. Exploration 1. Before class begins create 6 different stations around the room. At each station place one light source and mark on the wall (or provide measuring tape) increasing height measured in inches up to 35 inches. At one of the stations, include a light source plus the three different gels. If possible, try and make the room as dark as possible when the activity begins. 2. Provide each student with a Student Guide, a solar module, and a multimeter. 3. Have students gather in groups of 2-3 to complete the Student Guide. Solar Energy Green Box: Lesson 4 Waves and Solar Cell Technology 5

6 4. Students will rotate throughout the classroom to test at least 6 different light sources. Explanation 1. What are electromagnetic waves? 2. What does the frequency of a wave refer to? Give examples of different frequencies. 3. What frequency can your solar cells use? 4. How do different light sources affect the voltage produced by the solar cell? 5. Why does the intensity (or distance) of the light source make a difference in electrical output? 6. How does reflection or refraction affect the electrical output from the light sources? Scientific Vocabulary: Electromagnetic radiation: Electromagnetic radiation (e.g., radio, microwaves, light) can be modeled as a wave of changing electric and magnetic fields or as particles called photons. The wave model is useful for explaining many features of electromagnetic radiation, and the particle model explains other features. Quantum theory relates the two models. When light or longer wavelength electromagnetic radiation is absorbed in matter, it is generally converted into thermal energy (heat). Shorter wavelength electromagnetic radiation (ultraviolet, X-rays, gamma rays) can ionize atoms and cause damage to living cells. Photovoltaic materials emit electrons when they absorb light of a high-enough frequency. Frequency: The number of crests that pass a given point within one second is described as the frequency of the wave. One wave or cycle per second is called a Hertz (Hz), after Heinrich Hertz who established the existence of radio waves. A wave with two cycles that pass a point in one second has a frequency of 2 Hz. Photovoltaic effect: The creation of voltage or electric current in a material upon exposure to light. Wavelength: Electromagnetic waves have crests and troughs similar to those of ocean waves. The distance between crests is the wavelength. The shortest wavelengths are just fractions of the size of an atom, while the longest wavelengths scientists currently study can be larger than the diameter of our planet! Reflection: The change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves. Refraction: The change in direction of a wave due to a change in its transmission medium. Solar Energy Green Box: Lesson 4 Waves and Solar Cell Technology 6

7 Elaboration Allow students to once again gather in their groups. They will need to choose one light source. In this experiment students will be manipulating the light source using reflection (mirrors), refraction (magnifying glass), and transmission (changing distance). Lay out on a table 3 reflective materials and 3 magnifying materials, and measuring tape for each group to measure distance (unless the teacher has marked off distances on the wall already). Students will need to use all three mediums to complete their Student Guides. For the purposes of this lesson, the main objective is for students to understand that changes in distance, affect the amount of light (or other source of energy) that is falling on an object, such as the solar cell. Evaluation Formative: Qualitative Data During the experiments ask students why they think they are getting different results. Ask students if they think the wavelengths are shorter or longer based on the results? Or if the frequencies are higher or lower? Make sure students understand that shorter wavelengths equal higher frequencies and longer wavelengths equal lower frequencies. Ask students to explain why the higher distance of the light source makes a difference to the voltage produced? Based on what they know about how solar cells work, ask students what range of frequency the lights are that they are using. Summative: Quantitative Data Students will complete their Student Guides for teacher assessment. Understanding of different wavelengths: 25 Accurate description of how wavelengths and frequencies relate: 25 Understanding of wave behavior related to reflection, refraction, and transmission: 30 Clean-up Students need to return all materials and supplies to where they were originally for the next class. If it is the last class of the day, have students collect all materials and return to the Green Box. Closure See the last PPT slide to ask recap questions and check for understanding. Solar Energy Green Box: Lesson 4 Waves and Solar Cell Technology 7

8 Adaptations for ESL, Special Ed, or G.T. If desired, students can draw diagrams of how the light was impacted by the mirror, magnifier, and change in distances. Have students draw all the parts of their experiment and include the waves of light and how they were influenced. Management Strategy There are three activities in this lesson, two of which require students to move around the classroom, so it will be important for the teacher to set up for all activities and be well prepared for the lesson. This will aid the teacher in smoothly and efficiently moving from one task to another to minimize student disruption and keep everyone on task. Solar Energy Green Box: Lesson 4 Waves and Solar Cell Technology 8