Photons Flashcards
(10 cards)
1
Q
What is a blackbody?
A
An ideal absorber and emitter of radiation
2
Q
What are the properties of a black body?
A
Absorbs all incident radiation
Has an emissivity of 1
Emits isotropically
3
Q
What is the equation for energy density?
A
u=U/V=1/V ∫g(ω)< ε(ω) > dω
From 0 to infinity
< ε(ω) > is the expected energy value at w
4
Q
What is the density of states for a photon?
A
g(k)dk=Vk2/2π2 dk * 2
5
Q
Why does the density of states differ for a photon?
A
The factor of 2 accounts for the two polarisations of light
6
Q
What is the dispersion relation?
A
ω=ck
7
Q
Hiw are photns modelled?
A
As SHOs
εn=(n+1/2)ℏω
8
Q
What is the Wien displacement law?
A
λmaxT=2.897 mmK
9
Q
What is the CMB evidence for?
A
The Big Bang model
10
Q
What does CMB tell us about the universe?
A
The universe cools as it expands adiabatically
T3V=constant
