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Act3_sol - Period 3 Solutions Electromagnetic Waves Radiant...

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12/29/04 1 Period 3 Solutions: Electromagnetic Waves – Radiant Energy II 3.1 Applications of the Quantum Model of Radiant Energy 1) Photon Absorption and Emission The diagrams below illustrate an atomic nucleus and energy levels of the atom’s electrons (not drawn to scale). Diagram #1 shows a photon incident on an electron in an atom. In diagram #2, an electron in the atom has absorbed a photon and has moved to a higher energy level. Diagram #3 shows the atom emitting a photon of light and dropping to a lower energy level. Diagram #4 shows the same atom some time later, after the electron has emitted a second photon and dropped to an even lower energy level. Answer the questions below based on these diagrams. Time 1: An ultraviolet light photon is Time 2: The electron moves up absorbed by an electron. two energy levels. Time 3: The electron drops down one Time 4: The electron drops down one energy level and emits one more energy level and one photon of visible light. emits a second photon. Nucleus Electron Photon 1 Photon 2 Photon 3
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12/29/04 2 a) Does the absorbed photon #1 or the emitted photon #2 have more energy? __ Photon #1 ___ How do you know? The absorption of photon #1 causes the electron to move up two energy levels. The emission of photon #2 causes the electron to drop down only one energy level. b) Which photon has a larger frequency, the absorbed or either of the emitted photons? How do you know? The absorbed photon (photon #1) has a higher frequency. Photons with greater energy have a higher frequency. c) Which photon has a longer wavelength – the absorbed or the emitted photon? How do you know? The emitted photon has a longer wavelength. Photons with less energy and lower frequency have longer wavelengths. d) If the absorbed photon #1 is a photon of blue visible light, what color of light could emitted photon #2 be? The emitted photon could be any form of electromagnetic radiation with less energy than the photon of blue light that was absorbed. The emitted photon could be green, yellow, orange, or red light, depending on the amount of energy released when the electron changes energy levels. e) Compare the energy of photon #1 to the energies of photons #2 and #3. The law of conservation of energy tells us that the sum of the energies of the emitted photons #2 and #3 must equal the energy of the absorbed photon #1. 2) Ultraviolet Light and Fluorescence Your instructor will demonstrate the results of shining several types of radiant energy on fluorescent materials. a) What happens when an atom fluoresces? Photons in the ultraviolet are absorbed by the atom. Photons of visible light are then emitted by the atom as it cascades down to its ground state . b) Which light source works the best? _ ultraviolet_ c) Will a glow coil provide suitable light for the materials to fluoresce? _ No _ Why or why not?
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