324
DOC.
11
LECTURE ON ELECTRICITY
&
MAGNETISM
[p. 75]
Vector of the
energy
flow
-
&z%y)
4tz
dE
.
+
dt
heat
loss
= jSn.da.
Thus,
the
energy
principle
has
been
satisfied,
with
the
expression
for
the
energy being
the
same as
in
electrostatics.
The
law
of conservation of
momentum;
radiation
pressure.
dhc
m
--
=
X
v
dt
-----------
-----------
Law
of the
equality
of
action &
reaction Xn
=
0
From
this
22
m1--
=
0
for
complete
system.
-
dx]
It
Edx.
m,-:
=
const.
1
dt
_
cfxi
d
If external forces
-
m
-1
=
dt
^
1
dt
^
a
Can the
momentum
of
a
system
be
increased
by
internal electrom.
processes
(Can
a
system
start
moving by itself?)
We
must calculate
the
sum
of the
ponderomotive
forces
acting on
the
system.
Per unit
volume
jy£z
~jzhy
=
-
4nc
{
6t dt
ÖyJ
87t
dx(Öy
+
§z
]
1
f
d
_ .
d
_
.]
+
4n
+
i
2
x
8n dx
0
=
4?tc
|
dt
-*xP
+
*•
-
1
d(&x)
}
8ti dx