Radiation

Discussion

Heat radiation (as opposed to particle radiation) is the transfer of internal energy in the form of electromagnetic waves. For most bodies on the earth, this radiation lies in the infrared region of the electromagnetic spectrum.

stefan-boltzmann law

One of the first to recognize that heat radiation is related to light was the English astronomer William Herschel, who noticed in 1800 that if a thermometer was moved from one end of a prism produced spectrum to the other, the highest temperatures would register below the red band, where no light was visible. Because of this position, this form of radiation is called infrared (infra being the Latin word for below or within). Sometimes this kind of radiation is called "heat waves" but this is a misnomer. Recall that heat is the transfer of internal energy from one region to another. As all forms of electromagnetic radiation transfer internal energy, they could be called heat.

Stefan-Boltzmann Law

P = εσA(T4 − T04)

where σ [sigma] is called Stefan's constant, which was discovered experimentally by Josef Stefan (1835-1893) Austria in 1879 and ε [epsilon] is the emissivity.

σ =  2π5k4  =  π2k4  = 5.67 × 10−8 W/m2K4
15h3c2 60ℏ3c2

Disconnected thoughts that aren't quotes.

  Dark colors absorb more radiant energy than do light colors. The burns on this woman's skin mimic the pattern on her blouse. She was exposed to a monstrous dose of electromagnetic radiation from a nuclear blast. (Source: Unknown)

wien's displacement law

A more complete explanation of this law can be found in the section on Planck's law.

λmax =  hc   1
k xT

where x is the solution of

xex  − 5 = 0
ex − 1

x = 4.96511…

In shortened form

λmax = b
T

b = 2.898 … mmK

text

Temperature (or Effective Temperature) of Selected Radiant Sources
kelvin
temperature		 radiant energy source
2.73 cosmic background radiation
306 human skin
500 household oven at its hottest
660 minimum temperature for incandescence
770 dull red heat
1400 glowing coals, electric stove, electric toaster
1900 candle flame
2000 kerosene lamp
2800 incandescent light bulb, 75 W
2900 incandescent light bulb, 100 W
3000 incandescent light bulb, 200 W
3100 sunrise or sunset (effective)
3200 professional studio lights
3600 one hour after sunrise or one hour before sunset (effective)
4000 two hours after sunrise or two hours before sunset (effective)
5500 direct midday sunlight
6500 daylight (effective)
7000 overcast sky (effective)
20-30,000 lightning bolt

Transition paragraph

Metal Temperature by Color   Color Scale of Temperature
color approximate temperature   color Temperature
℉ ℃ K   ℃ K
faint red 930 500 770   incipient red heat 500 - 550 770 - 820
blood red 1075 580 855   dark red heat 650 - 750 920 - 1020
dark cherry 1175 635 910   bright red heat 850 - 950 1120 - 1220
medium cherry 1275 0690 0965   yellowish red heat 1050 - 1150 1320 - 1420
cherry 1375 0745 1020   incipient white heat 1250 - 1350 1520 - 1620
bright cherry 1450 0790 1060   white heat 1450 - 1550 1720 - 1820
salmon 1550 0845 1115   "This table is the result of an effort to interpret in terms of thermometric readings, the common expressions used in describing temperatures. It is obvious that these values are only approximations."
dark orange 1630 0890 1160
orange 1725 0940 1215
lemon 1830 1000 1270
light yellow 1975 1080 1355
white 2200 1205 1480
Sources: Process Associates of America & Handbook of Chemistry & Physics, 1924

Transition paragraph

Spectral Classification of Stars
color T (K) class discrete spectra examples
very blue 30,000 O He+, N++, Si+++,
other highly ionized atoms		 naos, mintaka
blue-white 20,000 B weak H;
He, Si+, Si ++, O+, Mg+		 spica, rigel
white 10,000 A strong H;
Mg+, Si+, Fe+, Ti+, Ca+		 sirius, vega
yellow-white 8000 F weak H; Ca+, Fe+, Cr+; Fe, Cr,
and other neutral metals		 canopus, procyon
yellow 6000 G strong Ca+; many neutral
and ionized metals; CH bands		 sun, alpha centauri
orange 4000 K CH bands;
neutral metals		 arcturus, aldebaran
red 3000 M molecular TiO bands;
neutral metals		 antares, betelgeuse

solar energy

greenhouse effect

History

The basic effect…


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Global temperature and atmospheric carbon dioxide trends match. The very long graph made popular by Al Gore in An Inconvenient Truth.


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Plot one against the other. The relation is approximately linear. Al Gore never did this one.


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Naturally occurring greenhouse gases whose concentrations are increasing due to human activities

Other naturally occurring greenhouse gases of lesser concern.

Greenhouse gases that do not occur naturally.

Indirect greenhouse gases

key infrared absorption bands in the atmosphere correspond to H2O, CO2, O3

Global Warming Properties of Selected Greeenhouse Gases
molecule global warming
potential
(CO2 = 1)		 atmospheric
lifetime
(years)		 raditative
forcing
(W/m2)		 radiative
efficiency
(W/m2ppb)
CO2 carbon dioxide 1 120 1.66 0.000014
CH4 methane 21 12 0.48 0.00037
N2O nitrous oxide 310 114 0.16 0.00303
CCl3F CFC-11 3,800 45 0.063 0.25
CF2Cl2 CFC-12 8,100 100 0.17 0.32
C2F3Cl3 CFC-113 4,800 85 0.024 0.3
CHClF2 HCFC-22 1,500 12 0.033 0.2
CCl4 carbon tetrachloride 1,400 26 0.012 0.13
CH3CCl3 methyl chloroform 146 5 0.0011 0.06
CHF3 HFC-23 11,700 270 0.0033 0.19
C2HF5 HFC-125 2,800 29 0.0009 0.23
C2H2F4 HFC-134a 1,300 14 0.0055 0.16
C2H4F2 HFC-152a 140 1.4 0.0004 0.09
SF6 sulfur hexafluoride 23,900 3,200 0.0029 0.52
SF5CF3 * 19,000 1,000 ? 0.59
H2O water, tropospheric ? ? ? ?
H2O water, stratospheric ? ? 0.02 ?
O3 ozone, tropospheric ? ? +0.35 ?
O3 ozone, stratospheric ? ? −0.15 ?
CO carbon monoxide ? 0.25 ? ?
H2 hydrogen ? ? ? ?
* trifluoromethyl sulphur pentafluoride Primary Source: IPCC

Temperatures are rising across the globe.


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