#16
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![]() Zeroth Law of Thermodynamics ![]() If two systems are in thermal equilibrium with a third system, then they must be in thermal equilibrium with each other.
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دكتور عاطف خليفة كيميائي 500 امتحان كيمياء |
#17
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Blackbody
A hypothetic body that completely absorbs all wavelengths of thermal radiation incident on it. Such bodies do not reflect light, and therefore appear black if their temperatures are low enough so as not to be self-luminous. All blackbodies heated to a given temperature emit thermal radiation with the same spectrum, as required by arguments of classical physics involving thermal equilibrium. However, the distribution of blackbody radiation as a function of wavelength, known as the Planck law, cannot be predicted using classical physics. This fact was the first motivating force behind the development of quantum mechanics
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دكتور عاطف خليفة كيميائي 500 امتحان كيمياء |
#18
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![]() Blackbody Radiation The thermal radiation emitted by a blackbody heated to a given temperature. All blackbodies heated to a given temperature emit thermal radiation with the same spectrum, known as the Planck law.
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دكتور عاطف خليفة كيميائي 500 امتحان كيمياء |
#19
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Blackbody Temperature
The effective temperature at which a blackbody emits blackbody radiation. Plack Energ ![]() The Planck energy is the average energy of an oscillator, ![]() The Planck postulate states that ![]() where n is a nonnegative integer, h is Planck's constant, and ![]() ![]() where C is a constant, k is Boltzmann's constant, and T is the temperature. Plugging in, ![]() Planck Intensity Density ![]() ![]() In terms of frequency, the energy flux from blackbody radiation is given by ![]() ![]() ![]() ![]() ![]() ![]() ![]() where ![]() ![]() ![]() is the number of cells per unit phase space. The factor of 2 must be added since two electrons with opposite spins may occupy the same element of phase space. The momentum of a photon is given by ![]() so ![]() and ![]() where ![]() ![]() ![]() ![]() ![]() ![]() Planck Law Planck Law ![]() ![]() ![]() ![]() ![]() The Planck law gives the intensity radiated by a blackbody as a function of frequency (or wavelength). Let a blackbody have temperature T. Let ![]() ![]() ![]() ![]()
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دكتور عاطف خليفة كيميائي 500 امتحان كيمياء |
#20
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وسنكمل ان شاء الله
يتبع
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دكتور عاطف خليفة كيميائي 500 امتحان كيمياء |
#21
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جزاك الله كل خير
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#22
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Planck Occupancy
In terms of frequency, ![]() and in terms of wavelength ![]()
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دكتور عاطف خليفة كيميائي 500 امتحان كيمياء |
#23
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Planck Postulate
Planck ![]() ![]() where n = 1, 2, 3, ..., h is Planck's constant, and ![]() ![]() ![]()
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#24
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Radiation Constant
![]() The constant related to the total energy radiated by a blackbody (i.e., the Stefan-Boltzmann law), and defined as ![]() ![]() ![]() ![]() ![]() where ![]() ![]() ![]() ![]() ![]() ![]()
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#25
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Radiometer Equation
![]() ![]() where ![]() ![]() ![]() ![]()
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#26
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Rayleigh-Jeans Law
![]() A classical law approximately describing the intensity of radiation emitted by a blackbody, derived by Rayleigh and Jeans by counting the number of standing wave modes in an enclosure. It corresponds to the Planck law in the case of small frequencies, in which case ![]() ![]() Plugging this into the Planck law gives ![]() ![]() ![]() ![]() ![]()
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#27
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شكرا ليك جدا
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