8—13.
THE GLOW DISCHARGE
175
A
“
normal
”
discharge occurs ina tube when, with small cur_
.
rent, the cathode glow covers only a portion of the cathode surface.
If the current is increased, this luminous
extends until the
—
_
entire surface is covered.
Beyond this point the discharge is
“
abnormal.”
For the condition of normal discharge, it has
'
found that the current density, i… is constant;
the area of the
cathode covered by the glow is strictly proportional to the t0tal
current
through the ”tube.
approximately, and within
restricted ranges of pressure (p), i,. =
where k is a constant.
This rule is exceedingly approximate.
«
_»
Further, with a normal discharge, it has been found that the
potential difference between the cathode and a point just in the
,
negative glow is a constant. This is called the na_rmal caiodefal[
_
of potential (Vn), and has a characteristic value for each
tion of gas and electrode material.
For platinum and oxygen, its
_
value is 364:
for a‘luminum‘and nitrogen 179 volts, for
,
and heliùm at pressures from 14 -to 0.6 millimeters, it rise_s from
153 to 158 volts.
V,.“ is least“ for the inért gases and with electrodes
of material having a low “work function. Very appr0ximately,
V,, = pd… where
is the length of the cathode dark space under
normal conditions.
This ru—l_eis exceedingly rough.
_
.
.
.
‘
The cat/fade dark space has,asharp boundary at the negative
.glow, of approximately the same‘ shape as that of the cathode.
Positive ions are formed—in this dark space andmove toward the
’cathode where, with other [possible agencies, they ej ect électrons.
The eleCtros,
from the rcath9de,…suffer
.
.
many
100) with the{gas' atoms «i—nthe- dark
_
_
space. _ ThecathodedarkSpaœlSâ-reglonOf pdsî‘tivespaœ Charge,
'
.
'
thenumberofposmvemnsexceedmgthe number of électrom,
JJThomson…studædtheelectmcaleldsmthlsdarkspaœ
'
"
'
:
'thrwghthwœgwnmmanelectmngun
Ï
—
"
10nsandelectmnsasmmYas1011Pefœblcœntlmetef0feach l ‘
-
.
havebeenbservedTheœnœntratwnfallso”ltheFafaaY
_,
: Î darkspacesothatelectr0nsm0V€mtwfmmthenegaüwgïow‘
THE GLOW DISCHARGE
175
A
“
normal
”
discharge occurs ina tube when, with small cur_
.
rent, the cathode glow covers only a portion of the cathode surface.
If the current is increased, this luminous
extends until the
—
_
entire surface is covered.
Beyond this point the discharge is
“
abnormal.”
For the condition of normal discharge, it has
'
found that the current density, i… is constant;
the area of the
cathode covered by the glow is strictly proportional to the t0tal
current
through the ”tube.
approximately, and within
restricted ranges of pressure (p), i,. =
where k is a constant.
This rule is exceedingly approximate.
«
_»
Further, with a normal discharge, it has been found that the
potential difference between the cathode and a point just in the
,
negative glow is a constant. This is called the na_rmal caiodefal[
_
of potential (Vn), and has a characteristic value for each
tion of gas and electrode material.
For platinum and oxygen, its
_
value is 364:
for a‘luminum‘and nitrogen 179 volts, for
,
and heliùm at pressures from 14 -to 0.6 millimeters, it rise_s from
153 to 158 volts.
V,.“ is least“ for the inért gases and with electrodes
of material having a low “work function. Very appr0ximately,
V,, = pd… where
is the length of the cathode dark space under
normal conditions.
This ru—l_eis exceedingly rough.
_
.
.
.
‘
The cat/fade dark space has,asharp boundary at the negative
.glow, of approximately the same‘ shape as that of the cathode.
Positive ions are formed—in this dark space andmove toward the
’cathode where, with other [possible agencies, they ej ect électrons.
The eleCtros,
from the rcath9de,…suffer
.
.
many
100) with the{gas' atoms «i—nthe- dark
_
_
space. _ ThecathodedarkSpaœlSâ-reglonOf pdsî‘tivespaœ Charge,
'
.
'
thenumberofposmvemnsexceedmgthe number of électrom,
JJThomson…studædtheelectmcaleldsmthlsdarkspaœ
'
"
'
:
'thrwghthwœgwnmmanelectmngun
Ï
—
"
10nsandelectmnsasmmYas1011Pefœblcœntlmetef0feach l ‘
-
.
havebeenbservedTheœnœntratwnfallso”ltheFafaaY
_,
: Î darkspacesothatelectr0nsm0V€mtwfmmthenegaüwgïow‘