146
7.
THE OUTER PARTS OF THE ATOM
Ï
millimeters for monatomic gases.
This may be shown by increas—
,
ing the pressure,
when the curves OP1, OP2, etc., may be obtained…”
These are found to rise above OP0 at the same potential
as'
_
in the former case.
[
.
This method is not Very satisfactory
since the potential at which OP1, OP2, etc.,
rise above the gas-free curve GP,, is not
_
;
sharply dened. It may be brought out more
,
|
’
clearly by heating the lament to such high
[,"
temperatures that a space charge always
!
exists between it and the plate. Now, when ,
_
{
positive ions and electrons are produced from
'
_
.|
_
neutral gas particles by collision, the elec—
Vf%
V%
trons
are
rapidly drawn away and the ;
FIG— 7—6Replot0fülata slower positive ions tend to neutrali2e the
Ï
for gure 7—4.
.
.
space charge, resulting in much greater ,
__
_
current ow.*
With the presence of a space charge, Langmuir’s
equation ] = B V
% holds true.
Hence, plotting ] against V% gives
a straight line. As ionization by collision sets in, there will be
_
deviation from this straight line as indicated in gure 7—6. This
*"9_,
'
,
…
:
,
,
B
©
.
—
Circuit for measuringionizing_potentials.
morer.pronounced than the one in gure 7—4. CorreC—
'_
t101mus'
for the initial velocityof emission of the elec—
,;trqnssacontaa . potentials,xlament drops—Of potential, etc; ,_
j
method for
ofsmall
.
,Jérï3** ;f
'
'
—