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Photoelectric Effect Apparatus
Model No. AP-8209
17
®
Experiment 3: Measuring Current-Voltage Characteristics
of Spectral Lines - Different Frequencies, Constant
Intensity
This section outlines the instructions for measuring and comparing the current versus voltage
characteristics of three spectral lines, 436 nm, 546 nm, and 577 nm, but with the same light
intensity.
Preparation for Measurement
1.
Cover the window of the Mercury Light Source enclosure with the Mercury Lamp Cap from
the Optical Filters box. Cover the window of the Photodiode enclosure with the Photodiode
Cap from the Optical Filters box.
2.
On the h/e Power Supply, turn on POWER and MERCURY LAMP. On the Photoelectric
Effect Apparatus, push in the POWER button to the ON position.
3.
Allow the light source and the apparatus to warm up for 20 minutes.
4.
On the apparatus, set the VOLTAGE Range Switch to –2 — +30 V. Turn the CURRENT
RANGES Switch to 10
-11
.
5.
To set the current amplifier to zero, first disconnect the ‘A’, ‘K’, and ‘down arrow’
(GROUND) cables from the back panel of the apparatus.
6.
Press the PHOTOTUBE SIGNAL button in to CALIBRATION.
7.
Adjust the CURRENT CALIBRATION knob until the current is zero.
8.
Press the PHOTOTUBE SIGNAL button to MEASURE.
9.
Reconnect the ‘A’, ‘K’, and ‘down arrow’ (GROUND) cables to the back of the
apparatus.
Measurement - Different Frequencies, Constant Intensity
436 nm Wavelength
1.
Uncover the window of the Photodiode enclosure. Place the 4 mm
diameter aperture and the 436 nm filter in the window of the
enclosure.
2.
Uncover the window of the Mercury Light Source enclosure. A
spectral line of 436 nm will shine on the cathode in the Photodiode
enclosure.
3.
Adjust the –2—+30 V VOLTAGE ADJUST knob so that the
current display is zero. Record the voltage and current in Table 4.
Note:
Always have a filter
on the window of the Pho-
todiode enclosure, and
put the cap on the Mer-
cury Light source when-
ever you change the filter
or aperture. Never let the
light from the Mercury
Light source shine
directly into the Photo-
diode enclosure.