PHYS 1C Lecture Notes - Lecture 18: Black-Body Radiation, Black Body, Emissivity
An object at any temperature emits
electromagnetic radiation (also called thermal
radiation).
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You are emitting radiation right now!
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A blackbody is an idealized system that absorbs all
incident radiation.
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It is opaque and non-reflective
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An object at any temperature emits
electromagnetic radiation (also called thermal
radiation)
-
Stefan's Law describes the total power radiated
for a blackbody and is given by
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Blackbody Radiation
Where P is the total power radiated, e is the emissivity of the object, A
is the surface area of the object, and T is the temperature of the object
in Kelvins.
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Sigma is the Stefan-Boltzmann constant
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Emissivity, e, measures how good of a radiator you are (0≤ε≤1). ε=1
for a black body
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The spectrum of radiation depends on the temperature of the object
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As the temperature increases, the peak of the intensity (Power/Area)
shifts to shorter wavelengths
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A blackbody is any body that is a perfect absorber or emitter of light.
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Λmax T = 2.898 x 10-3m K
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Where λmax is the wavelength at which the spectrum peaks
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T is the temperature in K of the object emitting the radiation
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The peak wavelength is inversely proportional to the absolute
temperature
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As T increases, the peak is "displaced" to shorter λ.
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The wavelengths of peak of the blackbody distribution was found to
follow Wien's Displacement Law:
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The observed emission from the Sun is similar to blackbody radiation
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Notice the spectrum at the top of the atmosphere differs from that at
sea level. Why?
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Much of the absorbed light leads to heating
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Blackbody radiator: Sun
(18) Lecture 28A: Quantum Mechanics
Monday, May 21, 2018
5:49 PM
week 7 Page 1
Document Summary
An object at any temperature emits electromagnetic radiation (also called thermal radiation). A blackbody is an idealized system that absorbs all incident radiation. An object at any temperature emits electromagnetic radiation (also called thermal radiation) Stefan"s law describes the total power radiated for a blackbody and is given by. Where p is the total power radiated, e is the emissivity of the object, a is the surface area of the object, and t is the temperature of the object in kelvins. Emissivity, e, measures how good of a radiator you are (0 1). The spectrum of radiation depends on the temperature of the object. As the temperature increases, the peak of the intensity (power/area) shifts to shorter wavelengths. A blackbody is any body that is a perfect absorber or emitter of light. The wavelengths of peak of the blackbody distribution was found to follow wien"s displacement law: Where max is the wavelength at which the spectrum peaks.
