EXPERIMENT 4—4.
(h/e)
_
95
The photoelectric cell C and the standard S… of gure 4—15
are -mounted on a
slide inside a black box so that either one
—
may
be shifted easily into the path of the light. The standard
may
be either; (l) a photo-cell of different nature than the
’
one under test (a potassium or a cesium cell, for example) which
has a known spectral distribution curve (supplied by the instructor
or
the manufacturer), or better, '(2) a ‘thermocouple of good
sensitivity operating into a galva‘nometer of low reSiStance, about
10 ohms.
.
_'
,
g
_ :
'Experiment;—4Observe the galvanometer d‘eectionÏs due to
the currents of the photoelectric cell C and
standard 8 for
each of ve or more wave-lengths chosen
over the
Visible spectrum.,
“
Galvanometer readings
”
shoùldî be the
difference between deections when the lamp is on and when it is
turned off.
Plot the ratio of thephotoelectric to
thermoelectric currents as ordinates and'the wave-lengths as“ abscissae.
If the standard is a photoelectric cell, the ratio of theburrent
of the unknown Cell to that of the Standard gives their comparative responses; and this ratio, multiplied by the. yield of the
standard, «ateach “wave—length, gives the yield of the “(Sell under
,
test,
Plot the yield-watve—lèngth curve.
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'
"
“;
THE RATÏO
CONSTANT TO THE
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CHARGE
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The
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ofd1fferentfrequenc1es ::See gure '
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4—8andequat1on4—IZ
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1
Âppamz‘us—Ad1agram oftheapparatusièp shown in fig—lire:
4—16Vanatwnssuchastheuse0f0therspectmmeter
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