DOC.
11
LECTURE ON ELECTRICITY
&
MAGNETISM
325
+
jybz
-
jz%y
=
_A|j_(£
ft
_(£
ft)
+
8t
(4nc
1
471
8
1
8
8
8x\
2
&
+
&)
+
3z
+
8
1
5
a
dx
\
2
__(£2+(£2)+
(g
g
)
+
(££)
9z
integrated
over
the
whole
system
[p. 76]
d^
dt
8
It
%*
K
i
47IC
-
(Sz§v)
3,
+ 3*
=
konst.
If
we
call
Qx
the
momentum
of the
electromagnetic field,
then
this tells
us
that the
sum
of the
mechanical
and the
electromagnetic
momentum in
a complete
system
is
constant.
Application
to
a plane wave
||
x-axis
Electric
force in Y-direction.
1
1
3.
I
Momentum that
impinges
on
the
surface l
per
unit time
=
-
This
is
equal
to
c
radiation
pressure.
Terms that
were
canceled
out in
integration.
Maxwell stresses.
The
momentum
transmitted
by
them
to
a
unit of
volume
per
unit
time
=
momentum transm. to mech.
system
+
increase of
momentum in
the element.
1Ä
=
curlS
-
i5.curl(S
a9'
c
dt
c
dt
dz dx
y