®
Model No. AP-8209
Photoelectric Effect Apparatus
8
h/e Photoelectric Effect Apparatus
The h/e Photoelectric Effect Apparatus has four knobs, three buttons and two digital displays on its
front panel, and four ports (labeled A, K, ‘down arrow’, and POWER SUPPLY) on its back panel.
The apparatus measures the photocurrent through the photodiode tube and the voltage across the
photodiode tube.
• Current Range switch: Sets the current range for the instrument’s current amplifier (10
-8
to 10
-13
A).
• Ammeter: Displays the photocurrent through the photodiode tube.
• Voltmeter: Displays potential across the photodiode tube.
• Voltage Range switch: Sets the voltage range as -2 to +30 V for plotting current-voltage characteristics
and -2 to +2 V for measuring the stopping potential.
• Power switch: Turns the power to the instrument ON or OFF.
• Voltage Adjust: Sets the potential across the photodiode tube for both voltage ranges.
• Current Calibration: Sets the current through the instrument to zero.
• Phototube Signal switch: Sets the signal from the photodiode tube to CALIBRATION or MEASURE.
Measurement Accuracy
Two factors may affect the measurement accuracy. First, the photocurrent is extremely small.
Second, because of the cathode dark current and the anode reverse current, the voltage when the
photocurrent is zero is not exactly the stopping potential. (For more information, see Experiments
in Modern Physics by A. Melissinos, copyright 1966, Harcourt Brace Jovanovich, publishers.)
The apparatus has a very sensitive and stable current amplifier so that the small photocurrent can be
measured accurately. The photodiode tube has a low level of dark current and anode reverse
voltage. In addition, because stopping potential versus frequency is plotted for several spectral lines
and the slope of stopping potential versus frequency is used to calculate Planck’s constant, the slope
method gives an accurate result even if the stopping potential is not exactly accurate.
AP-8209
PHOTOELECTRIC EFFECT APPARATUS
VOLTAGE
V
A
POWER
VOLTAGE ADJUST
CURRENT CALIBRATION
PHOTOTUBE SIGNAL
ON
OFF
-2 ~ +2 V
-2 ~ +30 V
CURRENT-VOLTAGE
CHARACTERISTICS
STOPPING
POTENTIAL
CALIBRATION
MEASURE
-2 V
+2 V
-2 V
+30 V
10
-13
10
-12
10
-11
10
-10
10
-9
10
-8
CURRENT RANGES
(Amps)
ZICY
Ammeter
Voltmeter
Voltage
Range
switch
Power
switch
Phototube Signal
switch
Current
Calibration
Voltage
Adjust
Current Range switch
Figure 4: Photoelectric Effect Apparatus