,
EXPERIMENÎË‘ 7—1
-
153
-
tiometer Will serve.
The grid voltmeter should be accurate and
should have a, nely divided scale. The usual B and C batteries
used in radio serve nicely for the grid and plate voltages. The
galvanometermay be one of the usual wall type With a sensitiveness
around 10”8 amperes and should be provided With a shunt.
'
With the switch on  and normal lament current or voltage,
slowly increase the grid voltage from zero, observing its values
simultaneously With the deections
the galvanometèr. Plot
With grid voltages as abscissae and positive ion currents (galvanometer readings) as ordinates. _
larger number of readings
be made where the galvànometer rst shows a deection.
galvanometer should be made as sensitive as possible in this
région, no attempt being made tomeasure the large currents which
are produced after ionization has set in. From the graph, determine the lowest grid voltage 71 at which the galvanometer Shows
any deection.
_
——
’
Repeat with the switch on B to obtain the voltage V2. The
'
mean of these two is the minimum ionizing potential of the gas
in the tube, neglecting corrections fOr-the initial velOcity of emis—
’
sion, contact potentials, etc. These usuallyamount
to about onehalf volt.
’
_
'
,
_
The
be performed using the ac tubes such
as
type 26 (low pOte—'ntial drop in the lament),
when _the values Vl
_
and 72 Will be ‘clOser
ac tubes Of the 27
-_
type:
In the latter,theènttig cathode is heated by an auxiliary‘ -
lament operated on e1theracordcandhenceis all _‘ at the same
,
potential, Thesw1tchÂBœdæpenssd With'_and
the nal graph
-is,Iike the dottedcurvelngure7—S
—
; j ,
.
,
;; Cofrect1onfor1n1tïalvelœltlesCtCmaybe
made if 1f-he' tube
t°
°aCh
.: t°fthewcœedmggasesr
…
'
-
'
EXPERIMENÎË‘ 7—1
-
153
-
tiometer Will serve.
The grid voltmeter should be accurate and
should have a, nely divided scale. The usual B and C batteries
used in radio serve nicely for the grid and plate voltages. The
galvanometermay be one of the usual wall type With a sensitiveness
around 10”8 amperes and should be provided With a shunt.
'
With the switch on  and normal lament current or voltage,
slowly increase the grid voltage from zero, observing its values
simultaneously With the deections
the galvanometèr. Plot
With grid voltages as abscissae and positive ion currents (galvanometer readings) as ordinates. _
larger number of readings
be made where the galvànometer rst shows a deection.
galvanometer should be made as sensitive as possible in this
région, no attempt being made tomeasure the large currents which
are produced after ionization has set in. From the graph, determine the lowest grid voltage 71 at which the galvanometer Shows
any deection.
_
——
’
Repeat with the switch on B to obtain the voltage V2. The
'
mean of these two is the minimum ionizing potential of the gas
in the tube, neglecting corrections fOr-the initial velOcity of emis—
’
sion, contact potentials, etc. These usuallyamount
to about onehalf volt.
’
_
'
,
_
The
be performed using the ac tubes such
as
type 26 (low pOte—'ntial drop in the lament),
when _the values Vl
_
and 72 Will be ‘clOser
ac tubes Of the 27
-_
type:
In the latter,theènttig cathode is heated by an auxiliary‘ -
lament operated on e1theracordcandhenceis all _‘ at the same
,
potential, Thesw1tchÂBœdæpenssd With'_and
the nal graph
-is,Iike the dottedcurvelngure7—S
—
; j ,
.
,
;; Cofrect1onfor1n1tïalvelœltlesCtCmaybe
made if 1f-he' tube
t°
°aCh
.: t°fthewcœedmggasesr
…
'
-
'