DOC. 4 KINETIC THEORY
LECTURE NOTES
149
2v-Xcosö
=
-In
^.dt-k
cost2
dz
4ir
dz
dF
=
--ncdtk^Lcos&sintidtidiö
4tc
dz
This
we
have to
integrate:[13]
a
from 0-2it, and
U
from 0 to
ni/2.
n
F
.
dG
sin3ö
1
1
.
dG
-
=
-nek- --nek
-
dt
dz
3
dz
o
1
i
dG
tr
=
--nek
-
3 dz
Free Path
Assume
again
that
all molecules
of
a given
kind have
the
same
velocity.
Collisions
of
a
moving
molecule
(radius
R1)
with
stationary
molecules
(radius
R2)
Collision
as soon as
the
distance
between
centers
R1
+
R2
=
O
Volume covered
in
unit time
Ttca2
[p. 4]
Number of
col.
of
a
molecule
of
kind
1
with
molecules of the
second kind
Z12 = n2izc1o2
Number of
collisions
of
mol.
of
kind
1
with mol.
of
kind
1
Z11 =
n1rc1s12,
where
s
is
the diameter of the molecule of
kind
1.
We
now
calculate
more
precisely by taking
into
account
the
fact
that the molecules that
are
hit
are
set in
motion.
First,
collisions
with molecules
of the kind
previously
emphasized
(dk)[14]