DEMO:

1
DEMO Black Body Radiation Heated Ball An
ideal blackbody absorbs all radiation incident
upon it, but we can use a metallic ball to
approximate such an object. As thermal energy is
added to an object, its temperature increases and
both the color and intensity of the emitted
radiation changes accordingly.
2
Blackbody Radiation All objects above
absolute zero absorb and emit electromagnetic
radiation (radiant energy) Hotter objects emit
more energy than colder objects (per unit area).
The amount of energy radiated is proportional to
the temperature of the object. The hotter the
object, the shorter the wavelength (?) of
emitted energy, the higher the frequency
different colors!
3
en.wikipedia.org/wiki/FileHuman-Infrar
ed.jpg
Much of a person's energy is radiated away in the
form of infrared energy. Some materials are
transparent to infrared light, while opaque to
visible light (note the plastic bag). Other
materials are transparent to visible light, while
opaque or reflective to the infrared (note the
man's glasses)
4
The color of stars is used to determine their
temperature ... Blue Stars 20,000 K
5
The wavelength of peak emission tells us the
temperature of the object!
"cold" dust
"cool" star
Sun
"hot" stars
frequency increases, wavelength decreases
6
A black body
A black body is a theoretical object that
absorbs 100 of the radiation that hits it.
Therefore it reflects no radiation and appears
perfectly black.
Stars are approximate black body radiators.
Most of the light directed at a star is absorbed.
It is therefore capable of absorbing all
wavelengths of electromagnetic radiation, so is
also capable of emitting all wavelengths of
electromagnetic radiation.