4.1 Basic Concepts and Formulae
249
Coefficient of diffusion ( D)
D =
η
ρ
(4.13)
Clausius Clepeyron equation
dP
dT
=
L
T (ν 2 − ν 1 )
(4.14)
where ν 1 and ν 2 are the initial and final specific volumes (volume per unit mass) and
L is the latent heat.
Vander Waal’s equation
P +
a
V 2
(V − b) = RT (for one mole of gas)
(4.15)
The Stefan-Boltzmann law
E = σ T
4
(4.16)
If a blackbody at absolute temperature T be surrounded by another blackbody at
absolute temperature T 0 , the amount of energy E lost per second per square metre
of the former is
E = σ (T
4
− T
4
0 )
(4.17)
where σ = 5.67 × 10
−8 W/m
2
.K
4 is known as Stefan-Boltzmann constant.
Maxwell’s thermodynamic relations
First relation:
∂ S
∂ V
T
=
∂ P
∂ T
V
(4.18)
Second relation:
∂ S
∂ P
T
= −
∂ V
∂ T
P
(4.19)
Third relation:
∂ T
∂ V
S
= −
∂ P
∂ S
V
(4.20)
Fourth relation:
∂ T
∂ P
S
=
∂ V
∂ S
P
(4.21)