Lesson 12 – Equations
12-1: Electromagnetic waves transport energy just like other waves and they are characterized
by their frequency v or wavelength λ. These two properties in a medium are related by:
c

v
c  c0 / n
c, the speed of propagation of a wave in that medium
c0  2.9979 108 m/s,
n, the index of refraction of that medium
n =1 for air and most gases, n = 1.5 for glass, and n = 1.33 for water
12.2 Energy of each photon
e  hv 
hc

where h 5 6.626069 × 10-34 J·s is (Planck’s constant).
12.3 Blackbody emissive power
Eb (T )   T 4
(W / m 2 )
  5.670 108 W / m 2  K 4
Stefan–Boltzmann constant
12.4 Planck’s law
Eb ( , T ) 
C1
 [exp (C2 / T )  1]
5
(W/ m 2   m)
C1  2 hc02  3.74177 108 W  μm 4 / m 2
C2  hc0 / k  1.43878 104 μm  K
k  1.38065 1023 J / K
Boltzmann’s constant
12.5 Wien’s displacement law
(T ) max power  2897.8 μm  K
12.6 Spectral hemispherical emissivity
  ( , T ) 
E ( , T )
Eb ( , T )
12.7 total blackbody emissive power
12.8 total blackbody emissive power
E (T )
 (T ) 

Eb (T )


0
  ( , T ) Eb ( , T )d 
T 4
12.9 Absorptivity, Reflectivity, and Transmissivity
Absorptivity:

Absorbed radiation Gabs

,0    1
Incident radiation
G
Reflectivity:

Reflected radiation Gref

,0    1
Incident radiation
G
Transmissivity:
 
Transmitted radiation Gtr

,0    1
Incident radiation
G