‘ ‘
: :,;lll—Ulll‘
100
s.
THERMIONIC EMISSION
-
and_that it is of the negative kind, since it can only pass through
the tube when the plate is positive.
_
-
The two—electrode vacuum tube, or
_
_
diode may be used as a rectier of
'
LI
_
l— | _ alternating currents since the ow of
1
"'"!
current through
it can only take place
in one direction, namely, from the hot
lament to the cold plate.*
5—2.
The Shot Eect.——In this sec'
tion we shall examine the proof that the
‘
'
negative electricity which leaves a hot
,
'
lament in a vacuum is made up of
many discrete charges rather than of an ’
unbroken stream of electricity. Assum‘
ing this to be true for the time being,
:
then the small electrical charges can be
'
!
thought of as bombarding the_positively ‘ _ î
.
:
,
charged plate of gure 5—1 like the small Î
,
shot from a shot gun.
The number of
_
‘
_
particles which reach the plate each
:
second
would
be
a
constant
when
_:
averaged over a suiciently long period
of time. This is found to be true since
[
the milliammeter readings, i of
f
_
5—1
,
do not uctu'ate.
If the current:
"
‘
.
could be examined during a very short
_
‘'
'
.time _interval and with a suic1ently
…
;
_
delicate instrument, .it would be found
Ï
,_
-
.
_
to increase and decrease slightly
_'r
g
.,
a
value.
It would further be:
Ÿ
fraction ofa
,
found thatthe changes around the
second
—"1
:,
value take place in an
manner
;
the exceSses and dec1€n':
fr0mP081üvetonegat1Ve °“tSldethe
…HOW6VT, in theW0rk’
°“thermwmcspresentedhere;th‘é
bè «that of the movmgelec
‘
'
……………… ……
!
…