Lecture 7 and 8 in class notes

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21 Jan 2011
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Lecture 7
273.15K = 0oC
Blackbody Curves, Ideal vs Reality
oA blackbody absorbs all radiation falling on it but then
reemits otherwise temperature would not change
oBlackbody curve represents intensity of radiation emitted by
any object over all possible frequencies
oThe peak emission wavelength decreases with temperature
oObject with the suns surface temperature peaks in the
visible spectrum
oThe total amount of energy emitted per unit area increases
temperature as fourth power
oComparison of blackbody curves of four cosmic objects. The
frequencies and
owavelengths corresponding to peak emission are marked.
oA cool, invisible galactic gas cloud called Rho Ophiuchi. At a
temperature
oof 60 K, it emits mostly low-frequency radio radiation.
oA dim, young star (shown red in the inset photograph) near
the center of
othe Orion Nebula. The stars atmosphere, at 600 K, radiates
primarily in the
oinfrared, here falsely coloured to represent differences in
temperature.
oThe Suns surface, at approximately 6000 K, is brightest in
the visible
oregion of the electromagnetic spectrum.
oSome very hot, bright stars in a cluster called Omega
Centauri, as
oobserved by a telescope aboard a space shuttle. At a
temperature of
o60,000 K, these stars radiate strongly in the ultraviolet.
(Harvard College
oObservatory; J. Moran; AURA; NASA)
Wiens Law
www.notesolution.com
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Document Summary

The frequencies and: wavelengths corresponding to peak emission are marked, a cool, invisible galactic gas cloud called rho ophiuchi. At a temperature: of 60 k, it emits mostly low-frequency radio radiation, a dim, young star (shown red in the inset photograph) near the center of, the orion nebula. Centauri, as: observed by a telescope aboard a space shuttle. At a temperature of: 60,000 k, these stars radiate strongly in the ultraviolet. (harvard college, observatory; j. moran; aura; nasa, wiens law www. notesolution. com o. T in kelvins: stefan blotzman law o, where sigma=5. 67x10-8w/m 2k 4, blackbody curves can be used as thermometers to determine the temperature ob distant objects, the sun"s surface temperature is about 5800k. What is the wavelength of the peak radiation of a blackbody with this temperature.  by stef law the solar energy flux per unit time is.  surface area of a sphere with sun radius is r=6. 96x105 km.

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