Only $2.99/month
Key Concepts:

Terms in this set (85)

1. All objects continually emit radiant energy over a range of λs.

2. Hotter objects emit more radiant energy than colder objects (per area) as quantified by the:
Stefan-Boltzmann Law:
E= σT^4
E: is the energy emitted by the body Watts m^-2
σ: is the Stefan Boltzmann constant
T: is the temperature of the body (K)
We use this relationship when examining: Infrared Imaging

3. The hotter the radiating object, the shorter is the λ of maximum emission, which is seen with:
Wien's Displacement Law:
λmax = C/T
λmax: wavelength (µ) of maximum radiation emitted
T : is the temperature of the object (K)
C: is Wien's constant 2898 µ K
This difference (displacement) allows us to refer to:
-Earth's (Terrestrial) Radiation as: Longwave Radiation
-Sun's (Solar) Radiation as: Shortwave Radiation
Although the sun emits at a maximum rate around 0.5 µ, it also emits radiation at other wavelengths as seen in the:
- Solar Electromagnetic Spectrum

Human's eyes are sensitive to radiation at wavelengths between 0.4 and 0.7 µ, this is called the:
- Visible Range

Which can be further divided into the colors of the spectrum
-Below the visual range are: Ultraviolet Wavelengths (7%)
- Above the visual range are: Infrared Wavelengths (49%)

4. Objects that are good absorbers of radiation at a particular λ are also good emitters at that same λ
(Kirchhoff's Law)

Some objects, called Blackbodies are unique in that they are both:
-Perfect emitters (emit 100% of the radiation possible for a given T)
-Perfect absorbers (absorb 100% of the radiation striking them)

-Both the Earth (70%) and the Sun (90%) approach being Blackbodies in their absorption and emission

-By contrast: the atmosphere does not act like a Black Body!

- Rather, all of the molecules of gases (N2, O2, H2O, etc) that comprise the atmosphere each act like: Selective Absorbers/Emitters
They absorbs/emit very well at some λ, but absorb/emit very poorly at other λ.