Chapter 3 Flashcards
What is power?
rate at which energy is flowing
expressed in watts
What is internal energy?
how fast the atoms and molecules in the object are moving
What is temperature?
measure of internal energy of an object
What are most temps of earth in K?
200k to 300k
How is energy transported from the sun to the earth?
electromagnetic radiation
What are the wavelengths of visible photons?
.4-.8 microns
What is Wien’s displacement law?
relation between an object’s temp and the peak of its emission spectrum
What is the Wien’s displacement equation?
λmax=2897/T
How does a lightbulb produce a higher fraction of visible photons?
run the filament at a higher temp
What is the meaning of the Stefan-Boltzmann equation?
total power radiated by a blackbody temp
What is the Stefan-Boltzmann equation?
P/a=σT^4
What is P/a?
power emitted by a blackbody per unit of surface area (w/m^2)
What is the Stefan-Boltzmann constant?
σ=5.67x10^-8 w/m^2/K^4
What is the 1st law of thermodynamics?
energy is conserved
What happens when energy in is greater than energy out?
internal energy and temp increase
What happens when energy out is greater than energy in?
internal energy and temp decrease
What happens when energy in equals energy out?
internal temp and energy don’t change: equilibrium
What are blackbodies?
body or surface that completely absorbs all radiant energy that falls upon it with no reflection
Surface that emits photons but we can’t see them
How can energy move?
energy can be absorbed, transmitted, reflected, or emitted
Can most infrared wavelengths pass through the atmosphere?
no, the atmosphere does not let eaves through equally (blocks some)
Does all visible light pass through the atmosphere?
yes
Where do incandescent light bulbs emit light?
1600-6000 K
What is thermal energy?
energy of motion
What is heat?
thermal energy transferred between 2 bodies with different temperaturese
Is there movement at 0 K?
no
What happens if there is more than 0 K?
there is movement of molecules
What happens if there is movement?
energy is emitted (photons)
Why don’t we see light when there is movement?
it is not in our visible range
What happens if there is an increase in speed of molecules?
there is light in our visible range
What is black?
light we can’t see
Where would a perfect blackbody be?
in complete darkness
Why do our eyes see blackbodies in light?
the light is reflecting in a range we can see
Is Earth a blackbody?
yes
What does the atmosphere let through?
visible light
What does the atmosphere only let some of through?
infrared radiation
Is the atmosphere a blackbody?
yes
