DOC.
11
LECTURE
ON ELECTRICITY
&
MAGNETISM
321
3©x
_
de2
_
diy
dt
dy
dz
dt
-------
---------------.
Besides this electromotive
field
we
also have
an
electric field
CxCyCz.
This has
been taken
over
from electrostatics. We
shall
therefore
call it
Csx
etc.
The
following
equations
hold
for
it
d&". d&
0
=
sz ~
~sy
dy
dz
--------------
--------------
Electromotive & electrostatic
field
are
both
def.
by
the
force
exerted
on
the
el. unit.
We
[p. 73]
have
therefore
no
reason
a priori
to
consider them
as being
of different
nature.
The
formal
laws also
require
that the
sum
tx
+ Csx
...
be considered
simply as
the
elec.
field
str.
Äx
...
For
if
one
adds
these
equations,
one
obt.
[
or
]
dBx
ddz
'
d&
dt
dy
dz
-----------------
or
--
=
curl
©.
dt
-----------------
d
($93
These
equations
give
-
(
--
+
•
+
•
)
=
0.
Thus,
they
are
compatible
with
the
dt
\ dx
condition
div
p
=
0
(There
is
no
real
magnetism).
Plane
waves.
z
Let
$
=
11%
&
2)
=
e€,
&
let
/x
&
e
be
indep.
of the
location.
Then the
equations
read:
*
We
are looking
for
waves
propagating
in
the
X-direction.
Everything
dep.
|
r
only on x
&
t.
Let
F(x
-
vt)
be
the
dependence
of all
components