"
__
'
,
'\««‘*“ä’
»
’
j
‘
%zrnm‘x‘ï"
‘
_
CHAPTER 5.
THERMIONIC EMISSION
_
_
5—1.
Introdüotion.——Aglass bulb containing a lament F and
a metal plate P, as in gure 5—1, is evacuated to a high degree.' In
the process of evacuation, gases are given o' continuously by the
walls of the_glass bulb and by the metals of the lament and plate.
In order to hasten the process, each of these parts is heated as hot
as possible while the pumps are in operation. The bulb is nally
sealed o" when the pressure has been reduced to 10*5 millimeter
of mercury or less. There are.’
'
_
_
still a large number of gas
.
molecules left in the bulb but,
_
- _
P
When compared With'the'num—‘
__
-
_
ber at “atmospheric pressure,
"
"
_
+
'
there are
few ‘ thatŸ the _‘
‘
_,
—î—
phenomena of _thermioniC emis—
=
'
E V
àon*Whièh
in ‘
,
_
'
:;
Will not
(
"
;
surably1nuencedThatthere
| Il !
°
“? Â
"
tr1c1ty left1nthembemaÿFrGS—IA two—electrode vacuum tube.
_‘
be shown by 1ncreas1ngth€
_
_
-
‘
»=
'
platevoltageV, whenthelament1scold
thousand
voltsareneededbeforeacurrentofelectnc1ty ”Will start" @ ow‘
_
"
”"lÿ throughtbetubeHed1dnotuseaplaœbatœrÿ(Vofgure5—l)
theposmSidebutmtwhentheCO…“‘«CÙŒYlwasmdê‘C@the
!
observedItlseVldentthatelectrl°lWlsgwen0”bÿthelament
‘
_