_6—3.
GRID CONTROL OF THE SPACE CHARGE 117
In the experimental work of testing the three-halves power law,
.
values of V should be taken as those of
"
the 'voltmeter plus
070 of gure 6—2 (about 1.5 volts). For the smaller
ages, near the lower end of the line in gure 6—3, variations from
linearity may occur due to the choice of a slightly incorrect value
‘
_
of V,,.
The cooling effect of the heavy lead—in wires of the lament
may also alter the emission siliciently so that the line is not
straight near the lower end. For higher voltages near the upper‘
end, the line Will curve over, aPproaching thehorizontal
saturation sets in. It is only in themiddle that the line Will be straight in
practice. Further, if a diode is used which has a directly heated
rather than an iridirectly heated
.
lament, there Will be an IR
'
drop along its length. The elec_
_
trons from one end of the la'
mentwill then be acted upon
l
'
'
.
_
.
’s
|3' _
—by a higher potential than those
bo
‘
-
.
from the other end. In this case .3
“g”
"
one may use the voltmeter— read—
_
_
-
_
‘
ing from the plate to the center
'
.
,
-of the lament as an “average.”
1
-
°
the potential dr0pin
?
__;
::
_
,
ment
13 comparable
to the plate
_
Log V
;,
voltage, the slope of
.
…
,
.
.
_
.
,
»
,
6—3.
Testing the
three-halves
.
W1ll be found …to be somewhere …
,;
_
power" law.
.
between 3/2
5/21t18,
…
—
«
—‘
’
…
.
.
'
Ï therefore,
cathode
_
TosumupthecurrentVOltagerelationofa
diode is acom._ _
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