’
4—6.
CURRENT—VOLTAGE CURVES
75
of accuracy.
In brief, a time lag in the surface photoelectric effect
has never been observed.
.
.
The current from a gas lled photoelectric cell decreases by as
'
much as twenty per cent when the frequency of the uctuations in
the light intensity is increased from zero to ten thousand cycles per
'
second; but this is a phenomenon due to the gas and not to any
nite emission time of the photo-electrons.
‘
'
4—6.
Current-voltage Curves.——Figure 4—7 shows curves of '
the photoelectric current for different applied voltages when the
'
incident light Was of constant intensity and
See
the circuit of gure 4—3. When the cathode or sensitive surface is
only slightly negative, the currents areSrnall. They quickly rise,
however, to a saturation value.— This is obviouSly a case where
a
.
,
:
.
s
,
G
'
.
‘
’
E
.
U
‘.
‘
x
%
-
e
8
oio'
_
,
_Ba'ery
+. —>
.
FIG. 4—7;
different volt—àgesapplied ‘to a vacuum
‘,.
_
,
,
*
,
‘
'
evæuàted
-
.
'
_
v theh1%herV01tages,lsduetotheeJë°tlonfel€CtmnsandPO—°dtlve
-
lonsfromneutralgasat0msbÿœlhsmwhleaccelefatedphoœ
‘
…7……1…91hhgh1