PASCO AP-8209 User manual

Instruction Manual
Manual No. 012-10626B
Photoelectric Effect
Apparatus
Model No. AP-8209

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Model No. AP-8209 Photoelectric Effect Apparatus
2
Table of Contents
Equipment List............................................................................................ 3
Introduction................................................................................................. 4
Background Information............................................................................ 4
Principle of the Experiment ....................................................................... 6
Basic Setup ................................................................................................. 6
Experiment 1: Measuring and Calculating Planck’s Constant............... 9
Experiment 2: Current-Voltage: Constant Frequency........................... 13
Experiment 3: Current-Voltage: Constant Intensity .............................. 17
Appendix A: Specifications ......................................................................21
Appendix B: DataStudio Instructions......................................................21
Appendix C: Technical Support, Copyright, Warranty ..........................23
Appendix D: Teacher’s Notes...................................................................23
Appendix E: Product End of Life Disposal Instructions........................27

Photoelectric Effect Apparatus Model No. AP-8209
3®
Photoelectric Effect Apparatus
Model No. AP-8209
Equipment List
Included Equipment
1. Optical Filters, Apertures, Caps, and Screws
2. Mercury Light Source Enclosure
3. Base
4. Photodiode Enclosure
5. Power Supply
6. Photoelectric Effect Apparatus
Cables and Cords
Power Cord for Power Supply
Power Cable for Photoelectric Effect Apparatus
BNC Connector Cable for Photodiode Enclosure
Banana-plug Patch Cords, Red and Blue
Items in the Optical Filters Box
7. Filters: 365 nm, 405 nm, 436 nm, 546 nm, 577 nm
8. Apertures: 2 mm diameter, 4 mm dia., 8 mm dia.
9. Caps: Photodiode, Mercury Lamp
1
2
4
3
5
6
7
8
9
9
Replacement Mercury Lamp: AP-8207
Replacement Photodiode: AP-8208

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Model No. AP-8209 Photoelectric Effect Apparatus
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Introduction
The photoelectric effect is the emission of electrons from the surface of a metal when
electromagnetic radiation (such as visible or ultraviolet light) of the right frequency shines on the
metal. At the time of its discovery, the classical wave model for light predicted that the energy of
the emitted electrons would increase as the intensity (brightness) of the light increased.
Instead it was discovered that the energy of the emitted electrons was directly proportional to the
frequency of the incident light, and that no electrons would be emitted if the light source was not
above a certain threshold frequency. Lower energy electrons were emitted when light with
relatively low frequency was incident on the metal, and higher energy electrons were emitted when
light with relatively high frequency was incident on the metal.
The AP-8209 Photoelectric Effect Apparatus consists of a mercury light source enclosure, a
photodiode tube enclosure, a base, the photoelectric effect test instrument, miscellaneous cords and
cables, a power supply for the mercury light source and the test instrument, and a box of apertures,
filters, caps, and alignment screws.
The apparatus has several important features:
• The current amplifier has high sensitivity and is very stable in order to improve the accuracy of the
measurement.
• The photoelectric tube has low levels of dark current and anode reverse current.
• The optical filters are of high quality in order to avoid an error due to interference between different
spectral lines.
Background Information
Many people contributed to the discovery and explanation of the photoelectric effect. In 1865
James Clerk Maxwell predicted the existence of electromagnetic waves and concluded that light
itself was just such a wave. Experimentalists attempted to generate and detect electromagnetic
radiation and the first clearly successful attempt was made in 1886 by Heinrich Hertz. In the midst
of his experimentation, he discovered that the spark produced by an electromagnetic receiver was
more vigorous if it was exposed to ultraviolet light. In 1888 Wilhelm Hallwachs demonstrated that
a negatively charged gold leaf electroscope would discharge more rapidly than normal if a clean
zinc disk connected to the electroscope was exposed to ultraviolet light. In 1899, J.J. Thomson
determined that the ultraviolet light caused electrons to be emitted from the metal.
In 1902, Phillip Lenard, an assistant to Heinrich Hertz, used a high intensity carbon arc light to
illuminate an emitter plate. Using a collector plate and a sensitive ammeter, he was able to measure
the small current produced when the emitter plate was exposed to light. In order to measure the
energy of the emitted electrons, Lenard charged the collector plate negatively so that the electrons
from the emitter plate would be repelled. He found that there was a minimum “stopping” potential
that kept all electrons from reaching the collector. He was surprised to discover that the “stopping”
potential, V, - and therefore the energy of the emitted electrons - did not depend on the intensity of
the light. He found that the maximum energy of the emitted electrons did depend on the color, or
frequency, of the light.

Photoelectric Effect Apparatus Model No. AP-8209
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In 1901 Max Planck published his theory of radiation. In it he stated that an oscillator, or any
similar physical system, has a discrete set of possible energy values or levels; energies between
these values never occur. Planck went on to state that the emission and absorption of radiation is
associated with transitions or jumps between two energy levels. The energy lost or gained by the
oscillator is emitted or absorbed as a quantum of radiant energy, the magnitude of which is
expressed by the equation: E = h ν where Eequals the radiant energy, ν is the frequency of the
radiation, and his a fundamental constant of nature. (The constant, h, became known as Planck's
constant.)
In 1905 Albert Einstein gave a simple explanation of Lenard’s discoveries using Planck’s theory.
The new ‘quantum’-based model predicted that higher frequency light would produce higher
energy emitted electrons (photoelectrons), independent of intensity,
while increased intensity would only increase the number of electrons
emitted (or photoelectric current). Einstein assumed that the light
shining on the emitter material could be thought of as ‘quanta’ of
energy (called photons) with the amount of energy equal to h ν with ν
as the frequency. In the photoelectric effect, one ‘quantum’ of energy
is absorbed by one electron. If the electron is below the surface of the
emitter material, some of the absorbed energy is lost as the electron
moves towards the surface. This is usually called the ‘work function’
(Wo). If the ‘quantum’ is more than the ‘work function’, then the
electron is emitted with a certain amount of kinetic energy. Einstein
applied Planck's theory and explained the photoelectric effect in
terms of the quantum model using his famous equation for which he
received the Nobel prize in 1921:
where KEmax is the maximum kinetic energy of the emitted photoelectron. In terms of kinetic
energy,
If the collector plate is charged negatively to the ‘stopping’ potential so that electrons from the
emitter don’t reach the collector and the photocurrent is zero, the highest kinetic energy electrons
will have energy eV where eis the charge on the electron and Vis the ‘stopping’ potential.
Einstein’s theory predicts that if the frequency of the incident
light is varied, and the ‘stopping’ potential, V, is plotted as a
function of frequency, the slope of the line is h/e (see Figure 1).
Eh ν KEmax W0 +==
KEmax h
ν W0 –=
eV h
ν W0 –=
Vh
e
---
ν
W0
e
--------
–=
Albert Einstein
Stopping
Potential, V
Frequency,
ν
Figure 1: Stopping Potential, V versus Frequency, ν

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Model No. AP-8209 Photoelectric Effect Apparatus
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Principle of the Experiment
When incident light shines on the cathode (K), photoelectrons can be
emitted and transferred to the anode (A). This constitutes a
photocurrent. By changing the voltage between the anode and cathode,
and measuring the photocurrent, you can determine the characteristic
current-voltage curves of the photoelectric tube.
The basic facts of the photoelectric effect experiments are as follows:
• For a given frequency (color) of light, if the voltage between the cathode
and anode, VAK, is equal to the stopping potential, V, the photocurrent is
zero.
• When the voltage between the cathode and anode is greater than the
stopping voltage, the photocurrent will increase quickly and eventually
reach saturation. The saturated current is proportional to the intensity of
the incident light. See Figure 2.
• Light of different frequencies (colors) have different stopping potentials.
See Figure 3
• The slope of a plot of stopping potential versus frequency is the value of
the ratio, h/e. See Figure 1.
• The photoelectric effect is almost instantaneous. Once the light shines on
the cathode, photoelectrons will be emitted in less than a nanosecond.
Basic Setup
Install the Mercury Lamp in the Mercury Light Source
Enclosure
• Use a phillips head screwdriver to remove the four small screws that hold the back
plate onto the Mercury Light Source enclosure.
• Use a small flat-blade screwdriver to pry the back panel off of the enclosure.
Note: Do not touch the glass envelope of the mercury lamp. Oil and moisture
from the skin may diminish the lamp’s performance. Use gloves, a clean cloth, or
a paper towel to handle the mercury lamp.
• Screw the mercury lamp into the socket inside the enclosure.
• Replace the back panel and screws on the enclosure.
V
A
AK
Anode
Cathode
Ammeter
Voltmeter
VAK
I
VAK
Intensity 1
Intensity 2
Stopping
Potential
Figure 2: Current vs. Intensity
I
VAK
Frequency 2
Frequency 1
Vstop 1
Vstop 2
Figure 3: Current vs. Frequency

Photoelectric Effect Apparatus Model No. AP-8209
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Alignment Screws
The Mercury Light Source has two small alignment screws on opposite
corners of its base. The Photodiode enclosure has slightly larger alignment
screws installed along the midline of its base.
Mount the Enclosures on the Base
Place the Mercury Light Source enclosure on the base so that the
alignment screws go into the matching alignment holes on the
base, and the position indicator arrow on the side of the enclosure
is aligned with 0 mm on the edge of the base.
Place the Photodiode enclosure on the base so that the alignment screws go
into the matching alignment holes on the slot in the base, and the position
indicator arrow on the side of the enclosure is aligned with 400 mm on the
edge of the base
Connect Cords and Cables
Note: Before connecting any cords or cables, be sure that both switches on
the h/e Power Supply are in the OFF position.
• Connect the power cord from the Mercury Light Source enclosure into the
receptacle labeled “POWER OUTPUT FOR MERCURY ~220V” on the side
of the h/e Power Supply.
• Connect the special DIN-plug-to-DIN-plug power cable between the port on
the back of the Photoelectric Effect Apparatus labeled “POWER SUPPLY” and
the port on the h/e Power Supply labeled “POWER OUTPUT FOR APPARATUS”. Screw the
knurled rings on the plug ends of the cable onto the threaded section of each port.
• Connect the special BNC-plug-to-BNC-plug cable between the port marked “K” on the Photodiode
enclosure and the port marked “K” on the back of the Photoelectric Effect Apparatus. Screw the
knurled rings on the plug ends of the cable onto the threaded section of each port.
• Connect the red banana-plug patch cord between the port marked “A” on the
Photodiode enclosure and the port marked “A” on the back of the Photoelectric
Effect Apparatus.
• Connect the blue banana-plug patch cord between the port marked with the ‘down
arrow’ (symbol for GROUND) on the Photodiode enclosure and the port marked
with the ‘down arrow’ (GROUND) on the back of the Photoelectric Effect
Apparatus.
• Connect the power cord between the port on the side of the h/e Power Supply
labeled “POWER INPUT ~110V” and an appropriate electrical outlet (Note: For
the 220 volt model, connect the cord between the port labeled “POWER INPUT ~220V” and an
appropriate electrical outlet.)
Alignment
screws
Alignment
holes
Alignment screws
Alignment holes
Note: These three
cords will be
disconnected during
calibration. You do
not need to turn off
the power from the
Power Supply when
you disconnect and
then reconnect these
three cords

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Model No. AP-8209 Photoelectric Effect Apparatus
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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
VA
POWER
VOLTAGE ADJUSTCURRENT CALIBRATIONPHOTOTUBE 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
(Am s)
ZICY
Ammeter Voltmeter
Voltage
Range
switch
Power
switch
Phototube Signal
switch
Current
Calibration
Voltage
Adjust
Current Range switch
Figure 4: Photoelectric Effect Apparatus

Photoelectric Effect Apparatus Model No. AP-8209
9®
Experiment 1: Measuring and Calculating Planck’s
Constant, h
Preparation before 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 to –2 — +2 V. Turn the
CURRENT RANGES switch to 10-13.
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
1. Uncover the window of the Photodiode enclosure. Place the 4 mm
diameter aperture and the 365 nm filter onto the window of the
enclosure. (See the sidebar note.)
2. Uncover the window of the Mercury Light Source. Spectral lines of
365 nm wavelength will shine on the cathode in the phototube.
3. Adjust the VOLTAGE ADJUST knob until the current on the
ammeter is zero.
4. Record the magnitude of the stopping potential for the 365 nm
wavelength in Table 1.
5. Cover the window of the Mercury Light Source.
Note: It is very important
to allow the light source
and apparatus to warm
up for 20 minutes prior to
making any measure-
ments.
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.

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Model No. AP-8209 Photoelectric Effect Apparatus
10
6. Replace the 365 nm filter with the 405 nm filter.
7. Uncover the window of the Mercury Light Source. Spectral lines of 405 nm wavelength
will shine on the cathode in the phototube.
8. Adjust the VOLTAGE ADJUST knob until the current on the ammeter is zero.
9. Record the magnitude of the stopping potential for the 405 nm wavelength in Table 1.
10. Cover the window of the Mercury Light Source.
11. Repeat the measurement procedure for the other filters. Record the magnitude of the
stopping potential for each wavelength in Table 1.
Calculating
1. Plot a graph of Stopping Potential (V) versus Frequency (x 1014 Hz).
Note: For information on using the DataStudio program to plot the graph, see
Appendix B.
2. Find the slope of the best-fit line through the data points on the
Stopping Potential (V) versus Frequency (x 1014 Hz) graph.
Note: The slope is the ratio of h/e, so Planck’s constant, h, is the product of
the charge of the electron (e = 1.602 x 10-19 C) and the slope of the best-fit
line.
According to the theory of linear regression, the slope of the Stopping Potential versus Frequency
graph can be calculated using the following equation:
where , , , and .
3. Record the calculated slope and use it to calculate the value of Planck’s constant, h.
Table 1: Stopping Potential of Spectral Lines, 4 mm diameter Aperture
Item 12345
Wavelength, λ(nm) 365.0 404.7 435.8 546.1 577.0
Frequency,
ν= c/λ, (x 1014 Hz) 8.214 7.408 6.879 5.490 5.196
Stopping Potential, V (V)
slope
ν V ν V⋅()–⋅
ν
2
ν
2
–
----------------------------------
=
ν
1
n
---
ν
i
i1=
n
∑
= ν
21
n
---
ν
i
2
i1=
n
∑
=V1
n
---Vi
i1=
n
∑
= ν V⋅1
n
---
ν
iVi
⋅
i1=
n
∑
=
Note: DataStudio allows
you to enter your data as
ordered pairs in a Table
display and then plot the
data in a Graph display.

Photoelectric Effect Apparatus Model No. AP-8209
11 ®
Slope = __________________
h= e x slope = _______________________
4. Estimate the error in the slope and round your result to the appropriate value. Compare
your calculated value of hto the accepted value, h0, 6.626 x 10-34 J s.
5. Record your percent difference ______________________
Questions
1. How does your calculated value of hcompare to the accepted value?
2. What do you think may account for the difference – if any – between your calculated
value of hand the accepted value?
3. How can you find the value of the Work Function from the graph of Stopping Potential
versus Frequency?
Extension
Repeat the data measurement and analysis procedure for the other two apertures in the OPTICAL
FILTERS box
Table 2: .Stopping Potential of Spectral Lines, 2 mm diameter Aperture
Table 3: .Stopping Potential of Spectral Lines, 8 mm diameter Aperture
Item 12345
Wavelength, λ(nm) 365.0 404.7 435.8 546.1 577.0
Frequency,
ν , (x 1014 Hz) 8.214 7.408 6.879 5.490 5.196
Stopping Potential, V (V)
Item 12345
Wavelength, λ(nm) 365.0 404.7 435.8 546.1 577.0
Frequency,
ν , (x 1014 Hz) 8.214 7.408 6.879 5.490 5.196
Stopping Potential, V (V)
percent difference = hh
0
–
h0
---------------x100

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Model No. AP-8209 Photoelectric Effect Apparatus
12
Questions
1. How does your calculated value of hfor each different aperture compare to the accepted
value, h0, 6.626 x 10-34 J s?
2. How does light intensity affect the Stopping Potential?

Photoelectric Effect Apparatus Model No. AP-8209
13 ®
Experiment 2: Measuring Current-Voltage Characteristics
of Spectral Lines - Constant Frequency, Different
Intensity
This section outlines the instructions for measuring and comparing the current versus voltage
characteristics of one spectral line at three different light intensities.
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 - Constant Frequency, Different Intensities
2 mm Aperture
1. Uncover the window of the Photodiode enclosure. Place the 2 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.
Note: It is very important
to allow the light source
and apparatus to warm up
for 20 minutes prior to
making any measure-
ments.
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.

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Model No. AP-8209 Photoelectric Effect Apparatus
14
3. Adjust the –2—+30 V VOLTAGE ADJUST knob so that the current display is zero.
Record the voltage and current in Table 4.
4. Increase the voltage by a small amount (for example, 1 V). Record the new voltage and
current in Table 4.
5. Continue to increase the voltage by the same small increment. Record the new voltage
and current each time in Table 4. Stop when you reach the end of the VOLTAGE range.
4 mm Aperture
1. Cover the window of the Mercury Light Source enclosure.
2. On the Photodiode enclosure, replace the 2 mm diameter aperture with the 4 mm diameter
aperture. Put the 436 nm filter back onto the window.
3. Uncover the window of the Mercury Light Source enclosure. A spectral line of 436 nm
will shine on the cathode in the Photodiode enclosure.
4. Adjust the –2—+30 V VOLTAGE ADJUST knob so that the current display is zero.
Record the voltage and current in Table 4.
5. Increase the voltage by a small amount (e.g., 1 V) and record the new voltage and current
in Table 4. Continue to increase the voltage by the same small increment and record the
new voltage and current each time in Table 4. Stop when you reach the end of the
VOLTAGE range
8 mm Aperture
1. Cover the window of the Mercury Light Source enclosure.
2. On the Photodiode enclosure, replace the 4 mm diameter aperture with the 8 mm diameter
aperture. Put the 436 nm filter back onto the window.
3. Uncover the window of the Mercury Light Source enclosure. A spectral line of 436 nm
will shine on the cathode in the Photodiode enclosure.
4. Adjust the –2—+30 V VOLTAGE ADJUST knob so that the current display is zero.
Record the voltage and current in Table 4.
5. Increase the voltage by a small amount (e.g., 1 V) and record the new voltage and current
in Table 4. Continue to increase the voltage by the same small increment and record the
new voltage and current each time in Table 4. Stop when you reach the end of the
VOLTAGE range.

Photoelectric Effect Apparatus Model No. AP-8209
15 ®
6. Turn off the POWER on the apparatus.Turn off the MERCURY LAMP power switch and
the POWER switch on the power supply. Return the apertures, filters, and caps to the
OPTICAL FILTERS box.
Analysis
1. Plot the graphs of Current (y-axis) versus Voltage (x-axis) for the one spectral line, 436 nm,
at the three different intensities.
Questions
1. How do the curves of current versus voltage for the one spectral line at three different
intensities compare? In other words, how are the curves similar to each other?
2. How do the curves of current versus voltage for the one spectral line at three different
intensities contrast? In other words, how do the curves differ from each other.
Table 4: Current and Voltage of Spectral Lines
λ= 435.8 nm
2 mm dia.
V (V)
I (x 10-11 A)
λ= 435.8 nm
4 mm dia.
V (V)
I (x 10-11 A)
λ= 435.8 nm
8 mm dia.
V (V)
I (x 10-11 A)

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Model No. AP-8209 Photoelectric Effect Apparatus
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Notes

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.

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Model No. AP-8209 Photoelectric Effect Apparatus
18
4. Increase the voltage by a small amount (for example, 1 V). Record the new voltage and
current in Table 5.
5. Continue to increase the voltage by the same small increment. Record the new voltage
and current each time in Table 5. Stop when you reach the end of the VOLTAGE range.
546 nm Wavelength
1. Cover the window of the Mercury Light Source enclosure.
2. On the Photodiode enclosure, replace the 436 nm filter with the 546 nm filter.
3. Uncover the window of the Mercury Light Source enclosure. A spectral line of 546 nm
will shine on the cathode in the Photodiode enclosure.
4. Adjust the –2—+30 V VOLTAGE ADJUST know so that the current display is zero.
Record the voltage and current in Table 5.
5. Increase the voltage by a small amount (e.g., 1 V) and record the new voltage and current
in Table 5. Continue to increase the voltage by the same small increment and record the
new voltage and current each time in Table 5. Stop when you reach the end of the
VOLTAGE range
577 nm Wavelength
1. Cover the window of the Mercury Light Source enclosure.
2. On the Photodiode enclosure, replace the 546 nm filter with the 577 nm filter.
3. Uncover the window of the Mercury Light Source enclosure. A spectral line of 577 nm
will shine on the cathode in the Photodiode enclosure.
4. Adjust the –2—+30 V VOLTAGE ADJUST know so that the current display is zero.
Record the voltage and current in Table 5.
5. Increase the voltage by a small amount (e.g., 1 V) and record the new voltage and current
in Table 54. Continue to increase the voltage by the same small increment and record the
new voltage and current each time in Table 5. Stop when you reach the end of the
VOLTAGE range.
6. Turn off the POWER on the apparatus.Turn off the MERCURY LAMP power switch and
the POWER switch on the power supply. Return the apertures, filters, and caps to the
OPTICAL FILTERS box.

Photoelectric Effect Apparatus Model No. AP-8209
19 ®
Analysis
1. Plot the graphs of Current (y-axis) versus Voltage (x-axis) for the three spectral lines, 436
nm, 546 nm, and 577 nm, at the one intensity.
Questions
1. How do the curves of current versus voltage for the three spectral lines at a constant intensity
compare? In other words, how are the curves similar to each other?
2. How do the curves of current versus voltage for the three spectral lines at a constant
intensity contrast? In other words, how do the curves differ from each other.
Table 5: Current and Voltage of Spectral Lines
λ= 435.8 nm
4 mm dia.
V (V)
I (x 10-11 A)
λ= 546.1 nm
4 mm dia.
V (V)
I (x 10-11 A)
λ= 577.0 nm
4 mm dia.
V (V)
I (x 10-11 A)

®
Model No. AP-8209 Photoelectric Effect Apparatus
20
Notes