|
The color of an object is depends upon its temperature as predicted by the
Stefan-Boltzmann law. This law describes the "ideal" blackbody
radiation given off by any object above absolute zero. Every objects emits
blackbody radiation although you do not normally notice it because our eyes are
only sensitive to a very small portion of the electromagnetic spectrum. An
object must be quite hot for it to emit visible light. For example, the heating
element on a stove glows "red hot." The Stefan-Boltzmann allows
us to determine the temperature by measuring the color spectrum given off
by the heating element. Our Sun is an another example of a "real"
blackbody radiator. It's spectrum isn't as smooth as the "ideal" ( it
is pitted and bumpy due to real-world conditions including, but not limited to,
absorption of the radiation en route to the earth) but it is close
enough. It fact, measuring color is the primary means astronomers
have of determining the temperatures of distant stars.
copyright: |
Temperature of the BlackBody applet can be set by using the provided
buttons or by moving the peak wavelength by click-dragging on the graph
itself. Temperature can be related to peak wavelength according to Wien's Law
--which can lead to
temperatures much in excess of 10,000 Kelvin. (Go to the Spiekbriefje
if you want to). Note the change in scale on
the y axis. The total energy radiated by a black body increases dramatically
with temperature although we autoscale the graph to highlight the change in
color.
- Vraagje: wat is de oppervlakte temperatuur van onze zon?
-
Waarom ligt de top van die grafiek midden in het gebied dat wij erg goed kunnen
zien?
- Hoe ziet het diagram van de maan eruit? ( let op: de
maan weerkaatst zonlicht én heeft zelf een oppervlakte temperatuur van
ongeveer 350 K).
A simulation of the visible spectrum is displayed under the curve,
corresponding to 400 (blue), 500 (green), and 600 (red) values. The colored
circles on the left represent the percent of each color present and a simulation
of the total color of the object.
|
