How do scientists use electromagnetic (EM) waves to analyze and understand the universe?
In this unit students learn about how scientists make knowledge claims about the size and composition of the universe. The communication of information from the far reaches of the universe, by electromagnetic waves, form the basis for these claims; and therefore the foundation for our understanding of stars, galaxies, and the possibility of extraterrestrial life. First, students investigate large distances using d=vt and time delays in radio communications. This leads to using the distance unit of light-years to express astronomical distances. Next, both reflecting and refracting telescopes are introduced to explain how these instruments use combinations of lenses and mirrors to magnify apparent size of the object. Third, using the properties of wavelength and frequency, the electromagnetic spectrum is introduced. This range of different electromagnetic waves, called the electromagnetic spectrum, is discussed as a continuum of wavelength, frequency, and energy which is categorized into groups depending upon their technological uses. The existence of other telescopes, besides light telescopes, that make use of the entire electromagnetic spectrum to analyze the universe are also introduced. Fourth, students make a diffraction grating spectroscope to observe spectral lines and measure the wavelength of a given frequency of light. This leads to a discussion of how the spectra of each element is unique and can be used to identify the chemical elements present in the outer layers of stars and galaxies thousands of light-years from earth. Then the nature and use of digital representations of information are explored. Analog and digital forms of communicating information are investigated and compared. This is an excellent opportunity to discuss the current decisions of scientists and policy makers to transition from analog and digital communications.
C2.4b Contrast the mechanism of energy changes and the appearance of absorption and emission spectra.
C2.4c Explain why an atom can absorb only certain wavelengths of light.
C2.4d Compare various wavelengths of light (visible and nonvisible) in terms of frequency and relative energy.
P1.2 Scientific Reflection and Social Implications
P1.2g Identify scientific tradeoffs in design decisions and choose among alternative solutions.
P1.2h Describe the distinctions between scientific theories, laws, hypotheses, and observations.
P1.2i Explain the progression of ideas and explanations that lead to science theories that are part of the current scientific consensus or core knowledge.
P1.2j Apply science principles or scientific data to anticipate effects of technological design decisions.
P1.2k Analyze how science and society interact from a historical, political, economic, or social perspective.
STANDARD P2: MOTION OF OBJECTS The universe is in a state of constant change. From small particles (electrons) to the large systems (galaxies) all things are in motion. Therefore, for students to understand the universe they must describe and represent various types of motion. Kinematics, the description of motion, always involves measurements of position and time. Students must describe the relationships between these quantities using mathematical statements, graphs, and motion maps. They use these representations as powerful tools to not only describe past motions but also predict future events.
P2.1 Position — Time
P2.1A Calculate the average speed of an object using the change of position and elapsed time.
P4.6 Electromagnetic Waves
P4.6A Identify the different regions on the electromagnetic spectrum and compare them in terms of wavelength, frequency, and energy.
P4.6B Explain why radio waves can travel through space, but sound waves cannot.
P4.6C Explain why there is a delay between the time we send a radio message to astronauts on the moon and when they receive it.
P4.6D Explain why we see a distant event before we hear it (e.g., lightning before thunder, exploding fi reworks before the boom).
P4.6x Electromagnetic Propagation
P4.6f Explain how radio waves are modified to send information in radio and television programs, radiocontrol cars, cell phone conversations, and GPS systems.
P4.6h Explain the relationship between the frequency of an electromagnetic wave and its technological uses.
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- How are electromagnetic waves described and measured?
- How is the entire electromagnetic spectrum used to 'measure' and analyze the universe?
- How do combinations of lenses and/or mirrors produce images in light telescopes?
- How do scientists use all forms of electromagnetic radiation and spectra to infer the composition and nature of stars?
- How are digital communications (images, sounds, text, etc.) different from analog communications?
- Why are there noticeable time delays in radio communications between the earth and the moon?
emission (line) spectrum
speed of light
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