UH PHYS 1302 - Ch30 (13 pages)

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Ch30



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Ch30

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ch 30 study guide


Pages:
13
School:
University of Houston
Course:
Phys 1302 - Introductory to Physics II

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Chapter 30 Quantum Physics 1 Blackbody Radiation and Planck s Hypothesis of Quantized Energy A blackbody is an idealized object that absorbs all incident radiation A blackbody at a fixed temperature T is a perfect emitter of radation The distribution of the amount of radiation given off by a blackbody of temperature T versus the frequency of the radiation f is shown in the figure This distribution is the same for any blackbody regardless of the material from which the blackbody is made It only depends on the temperature 1 As the temperature increases the total amount of energy radiated area under the curve increases Hotter objects radiate more energy L Whitehead 1 Phys 1302 2 As the temperature increases the peak frequency the frequency at which the blackbody emits the most energy increases The relationship between the peak frequency and temperature is given by Wien s displacement law fpeak 5 88 1010 sK 1 T 1 Kelvin K is a unit of temperature TK TC 273 15 where TK is the temperature in Kelvin and TC is the temperature in Celsius This relationship means that the color of a hot object is related to its temperature A hot stovetop appears red An object that glows red is at a lower temperature than an object that glows blue because fred fblue The sun has a surface temperature of 5800 K What is the peak frequency of radiation emitted by the Sun fpeak 5 88 1010 sK 1 T 5 88 1010 sK 1 5800K 3 4 1014 Hz This is in the infrared portion of the EM spectrum Blackbody radiation was understood experimentally in the late 1800 s but a theoretical explanantion for the results couldn t be found based on classical physics German physicist Max Planck was finally able to derive an expression for the frequency spectrum by making this assumption The radiation energy of a blackbody at frequency f must be an integral multiple of a constant h times the frequency En nhf n 0 1 2 3 2 We say that the energy is quantized It is not a continuous spectrum the energy can only take on certain values



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