Lecture8 - Homework #3 Multiple choice questions due...

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Homework #3 Multiple choice questions due Friday, February 10, 5:00 pm. Short answer questions due Monday, February 13, 2:30 pm Exam #1 Wednesday, February 15
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Radiative Energy: E = hc / λ or E = hf λ is the wavelength f is the frequency c is the speed of light h is the Planck Constant Shorter wavelength light carries more energy per photon.
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Light as Information Bearer The spectrum of an object can reveal the object’s: Composition Temperature Velocity Spectrum: light separated into its different wavelengths. Spectroscopy: The quantitative analysis of spectra
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Four Ways in Which Light can Interact with Matter 1. emission – matter releases energy as light 2. absorption – matter takes energy from light 3. transmission – matter allows light to pass through it 4. reflection – matter repels light in another direction The type of interaction is determined by  characteristics of the “matter” and  the  wavelength of light.
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Three ways in which spectra manifest themselves: Continuous spectra Absorption spectra Emission line spectra
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Continuous spectra are usually related to the temperature of an object that is emitting radiation. Absorption & emission line spectra are related to the composition of the material absorbing or emitting radiation.
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Kirchhoff’s Laws 1. A hot, dense glowing object (solid or  gas) emits a continuous spectrum.
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Kirchhoff’s Laws 2. A hot, low density gas emits light of  only certain wavelengths – an emission  line spectrum.
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Kirchhoff’s Laws 3. When light having a continuous spectrum passes through a cool gas, dark lines appear in the continuous spectrum – an absorption line spectrum.
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1. Hotter objects emit more total radiation per unit surface area. 1. Hotter objects have their peak radiation at shorter wavelengths (they will appear “bluer”) Rules for Thermal Emission by Opaque Objects
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The sun emits its peak radiation in the yellow portion of the visible spectrum At “room temperature”, or “body- temperature”, an object emits its peak radiation in the infrared.
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unit surface area. 1. Hotter objects have their peak radiation at
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This note was uploaded on 02/21/2012 for the course AST-A 105 taught by Professor Dr.dash during the Spring '12 term at Indiana.

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Lecture8 - Homework #3 Multiple choice questions due...

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