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Electromagnetic Spectrum and Telescopes Name: __________________________________________ Tentative Test Date: _______________ Unit 5: Electromagnetic Spectrum and Telescopes Definitions: Electromagnetic Spectrum regions: Amplitude Frequency Spectroscopy Radio waves Absorption Photon Speed of light (c) Microwave Electromagnetic radiation Radio telescope Telescope Infrared Electromagnetic spectrum Reflection Radiation Visible light Emission Refraction Wavelength Ultraviolet X-rays Gamma rays Can you…? 1. Match the vocabulary terms provided on the unit plan to their definitions. 2. Read the assigned readings and answer the questions provided. 3. Memorize the speed of light as 3.0x10 8 m/s. 4. If given wavelength or frequency, calculate the missing variable. 5. Characterize the different areas of the electromagnetic spectrum. 6. Construct a diagram of the electromagnetic spectrum and label the regions and their wavelengths and frequencies. 7. If given wavelength or frequency, determine the radiation type. 8. Explain why the sky appears blue. 9. Use a telescope to make observations of the sky. 10. Describe how observing methods that use radiation beyond the visual range have affected astronomy and our comprehension of the universe. 11. Describe the roles of telescopes and photography in advancing our knowledge of astronomy. Readings: • Light (ART5.1) • The Electromagnetic Spectrum (ART 5.2) Electromagnetic Spectrum and Telescopes Questions to answer LIGHT ART 5.1 1. What was the difference between the theory of light proposed by Christian Huygens and the theory proposed by Issac Newton? 2. What evidence supported the wave theory? 3. What did James Clerk Maxwell show? 4. Visible light is a form of what type of radiation? 5. Why does the quantum theory of light successfully explain all aspects of the behavior of light? 6. How was the speed of light determined and what is its value? 7. Is the speed of light the same in all mediums? Explain. 8. What is the difference between a luminous body and an illuminated body? 9. What causes the colors of opaque objects? The Electromagnetic Spectrum and Telescope ART 5.1: LIGHT The Nature of Light The wave theory received additional support from the electromagnetic theory of James Clerk The scientific study of the behavior of light is Maxwell (1864), who showed that electric and called optics and covers reflection of light by magnetic fields were propagated together and that a mirror or other object, refraction by a lens or their speed was identical with the speed of light. It prism, diffraction of light as it passes by the thus became clear that visible light is a form of edge of an opaque object, and interference electromagnetic radiation, constituting only a patterns resulting from diffraction. Also small part of the electromagnetic spectrum. studied is the polarization of light. Any Maxwell's theory was confirmed experimentally successful theory of the nature of light must with the discovery of radio waves by Heinrich be able to explain these and other optical Hertz in 1886. phenomena. Modern Theory of the Nature of Light The Wave, Particle, and Electromagnetic Theories of Light With the acceptance of the electromagnetic theory of light, only two general problems remained. One The earliest scientific theories of the nature of of these was that of the luminiferous ether, a light were proposed around the end of the 17th hypothetical medium suggested as the carrier of cent. In 1690, Christian Huygens proposed a light waves, just as air or water carries sound theory that explained light as a wave waves. The ether was assumed to have some very phenomenon. However, a rival theory was unusual properties, e.g., being massless but offered by Sir Isaac Newton in 1704. Newton, having high elasticity. A number of experiments who had discovered the visible spectrum in performed to give evidence of the ether, most 1666, held that light is composed of tiny notably by A. A. Michelson in 1881 and by particles, or corpuscles, emitted by luminous Michelson and E. W. Morley in 1887, failed to bodies. By combining this corpuscular theory support the ether hypothesis. With the publication with his laws of mechanics, he was able to of the special theory of relativity in 1905 by explain many optical phenomena. Albert Einstein, the ether was shown to be unnecessary to the electromagnetic theory. For more than 100 years, Newton's corpuscular theory of light was favored over The second main problem, and the more serious the wave theory, partly because of Newton's of the two, was the explanation of various great prestige and partly because not enough phenomena, such as the photoelectric effect, that experimental evidence existed to provide an involved the interaction of light with matter. adequate basis of comparison between the two Again the solution to the problem was proposed theories. Finally, important experiments were by Einstein, also in 1905. Einstein extended the done on the diffraction and interference of quantum theory of thermal radiation proposed by light by Thomas Young (1801) and A. J. Max Planck in 1900 to cover not only vibrations Fresnel (1814–15) that could only be of the source of radiation but also vibrations of the interpreted in terms of the wave theory. The radiation itself. He thus suggested that light, and polarization of light was still another other forms of electromagnetic radiation as well, phenomenon that could only be explained by travel as tiny bundles of energy called light the wave theory. Thus, in the 19th cent. the quanta, or photons. The energy of each photon is wave theory became the dominant theory of directly proportional to its frequency. the nature of light. 5: The Electromagnetic Spectrum and Telescope Page 1 of 2 ART 5.1: LIGHT With the development of the quantum theory relativity predicts that the speed of light in a of atomic and molecular structure by Niels vacuum is the limiting velocity for material Bohr and others, it became apparent that light particles; no particle can be accelerated from rest and other forms of electromagnetic radiation to the speed of light, although it may approach it are emitted and absorbed in connection with very closely. Particles moving at less than the energy transitions of the particles of the speed of light in a vacuum but greater than that of substance radiating or absorbing the light. In light in some other medium will emit a faint blue these processes, the quantum, or particle, light known as Cherenkov radiation when they nature of light is more important than its wave pass through the other medium. This phenomenon nature. When the transmission of light is has been used in various applications involving under consideration, however, the wave nature elementary particles. dominates over the particle nature. In 1924, Louis de Broglie showed that an analogous Luminous and Illuminated Bodies picture holds for particle behavior, with moving particles having certain wavelike In general, vision is due to the stimulation of the properties that govern their motion, so that optic nerves in the eye by light either directly there exists a complementarity between from its source or indirectly after reflection from particles and waves known as particle-wave other objects. A luminous body, such as the sun, duality. The quantum theory of light has another star, or a light bulb, is thus distinguished successfully explained all aspects of the from an illuminated body, such as the moon and behavior of light. most of the other objects one sees. The amount and type of light given off by a luminous body or The Speed of Light reflected by an illuminated body is of concern to the branch of physics known as photometry (see An important question in the history of the also lighting). Illuminated bodies not only reflect study of light has been the determination of its light but sometimes also transmit it. Transparent speed and of the relationship of this speed to objects, such as glass, air, and some liquids, allow other physical phenomena. At one time it was light to pass through them. Translucent objects, thought that light travels with infinite speed— such as tissue paper and certain types of glass, i.e., it is propagated instantaneously from its also allow light to pass through them but diffuse source to an observer. Olaus Rømer showed (scatter) it in the process, so that an observer that it was finite, however, and in 1675 cannot see a clear image of whatever lies on the estimated its value from differences in the other side of the object. Opaque objects do not time of eclipse of certain of Jupiter's satellites allow light to pass through them at all. Some when observed from different points in the transparent and translucent objects allow only earth's orbit. More accurate measurements light of certain wavelengths to pass through them were made during the 19th cent. by A. H. L. and thus appear colored. The colors of opaque Fizeau (1849), using a toothed wheel to objects are caused by selective reflection of interrupt the light, and by J. B. L. Foucault certain wavelengths and absorption of others. (1850), using a rotating mirror. The most accurate measurements of this type were made by Michelson. Modern electronic methods have improved this accuracy, yielding a value of 2.99792458 × 108 m (c.186,000 mi) per sec for the speed of light in a vacuum, and less for its speed in other media. The theory of 5: The Electromagnetic Spectrum and Telescope Page 2 of 2 ART 5.2 Electromagnetic Spectrum Measuring the electromagnetic spectrum You actually know more about it than you may think! The electromagnetic (EM) spectrum is just a name that scientists give a bunch of types of radiation when they want to talk about them as a group. Radiation is energy that travels and spreads out as it goes-- visible light that comes from a lamp in your house and radio waves that come from a radio station are two types of electromagnetic radiation.
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