Franck Hertz Experiment Manual SE 9639 PDF
Franck Hertz Experiment Manual SE 9639 PDF
Franck Hertz Experiment Manual SE 9639 PDF
Franck-Hertz Experiment
Model SE-9639
® ii
Instruction Manual 012-14264A
Franck-Hertz Experiment
SE-9639
Select:
Select: MEASURE
CURRENT Adjust:
RANGES CURRENT CALIBRATION
4
Select:
-4.5 V – 0 V
3
-4.5 V – +30 V
2
1
Adjust: Select:
0 – 100 V 0 – 100 V
Adjust: Adjust:
0 – 6.3 V -4.5 V – 0 V Adjust: and
0 – 200 V 0 – 200 V
and 0 – 12 V
-4.5 V – +30 V 5, 6, 7, 8
Equipment List
012-14264A 1
SE-9639 Franck-Hertz Experiment
Recommended Items
Safety Information
WARNING: To avoid possible electric shock or personal history, follow these guidelines.
2 012-14264A
Franck-Hertz Experiment Electrical Symbols
• Special note: If a dangerous voltage is applied to an input terminal, then the same voltage may occur at all
other terminals.
Electrical Symbols
Alternating Current
Direct Current
Chassis Ground
Fuse
On (Power)
Off (Power)
WARNING:
To reduce the risk of electric shock or damage to the instrument, turn the power switch off and
disconnect the power cord before replacing a tube.
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SE-9639 Franck-Hertz Experiment
Note: Replace the argon tube with the same type: Model SE-9645 Franck-Hertz Ar-Tube.
Fuse Replacement
WARNING
The fuse is inside a
To reduce the risk of electric shock or
tray. Open the
cover to remove damage to the instrument, turn the
the fuse. power switch OFF and disconnect the
power cord before replacing a fuse.
Note: Replace the burned fuses with new fuses of the same type. (One spare fuse is included.)
4 012-14264A
Franck-Hertz Experiment Introduction
Introduction
In 1914, James Franck and Gustav Hertz discovered in the course of their investigations an “energy loss in distinct steps
for electrons passing through mercury vapor”, and a corresponding emission at the ultraviolet line (= 254 nm) of mer-
cury. As it is not possible to observe the light emission directly, demonstrating this phenomenon requires extensive and
cumbersome experiment apparatus. They performed this experiment that has become one of the classic demonstrations
of the quantization of atomic energy levels. They were awarded the Nobel Prize for this work in 1925.
In this experiment, we will repeat Franck and Hertz's energy-loss observations, using argon, and try to interpret the data
in the context of modern atomic physics. We will not attempt the spectroscopic measurements, since the emissions are
weak and in the extreme ultraviolet portion of the spectrum.
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SE-9639 Franck-Hertz Experiment
When an electron has an inelastic collision with an argon atom, the kinetic
energy lost to the atom causes one of the outer orbital electrons to be
pushed up to the next higher energy level. This excited electron will within
a very short time fall back into the ground state level, emitting energy in
the form of photons. The original bombarding electron is again accelerated
toward the grid anode. Therefore, the excitation energy can be measured in
two ways: by the method outlined above, or by spectral analysis of the
radiation emitted by the excited atom.
• As a matter of fact, a strong line can be found for emission and absorption corresponding to an energy of e•U0, the exci-
tation energy of argon, in the optical spectrum (108.1 nm).
In figure 2, the resonance voltage is denoted by U0.
e•U0 = hƒ = hc/
or
U0
h = e ------
c
where e is the charge on an electron, h is Planck’s Constant, and c is the speed of light.
6 012-14264A
Franck-Hertz Experiment Connect Cables and Cords
Note: Before connecting any cords or cables, be sure that all power switches on the
Power Supplies and Current Amplifier are in the OFF position and all voltage con-
trols are turned fully counterclockwise.
See the next page for numbered instructions about connecting cables and cords.
SE-6621
SE-9650 Current Amplifier
Argon Tube
Enclosure
1.
Analog Port A
1.
12 V DC Output
2.
3. SE-9644
Power supply II
4.
100 V DC Output
2. 3.
Analog Port B
5.
SE-6615
Power Supply I
0 – 6.3 V DC Output
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SE-9639 Franck-Hertz Experiment
1. On the DC Current Amplifier, connect the special BNC-to-BNC cable between the port on the amplifier marked “INPUT
SIGNAL” and the port on the Argon Tube Enclosure marked “A”.
2. On Power Supply II, (SE-9644) connect the positive terminal of the 12 V DC output to the grid-like electrode labeled
“G2” (red sockets) on the Argon Tube Enclosure (SE-9650) and connect the negative terminal of the 12 V DC output to
the terminal labeled “A” (black sockets) on the enclosure.
3. On Power Supply II, connect the positive terminal of the 100 V DC output on the power supply to the grid-like electrode
labeled “G2” (red sockets) on the Argon Tube Enclosure and connect the negative terminal of the power supply to the ter-
minal labeled “K” (black sockets) on the enclosure.
4. On Power Supply I (SE-6615), connect the positive terminal of the -4.5 – +30 V DC output on the power supply to the
grid-like electrode labeled “G1” on the Argon Tube Enclosure and connect the negative terminal of the power supply to
the terminal labeled “K” (black sockets) on the enclosure,
5. On Power Supply I, connect the positive terminal of the 0 – 6.3 V DC output on the power supply to the red socket of the
port labeled “FILAMENT” on the Argon Tube enclosure and connect the negative terminal of the power supply to the
black socket of the “FILAMENT” port.
• Note: Before connecting the power cords, please check that the setting for the input voltage range (110 – 120 V or 220 –
240 V) matches the local AC voltage. For the two power supplies and the current amplifier, connect a power cord between
the port on the back labeled “AC POWER CORD” and an appropriate electrical outlet.
DANGER:
High Voltage is applied to the Argon Tube. Avoid contact with any part of the body.
• Only use safety equipment leads (shrouded patch cords) for connections.
• Make sure that the power supplies and current amplifier are OFF before making the connections.
• Make sure that the power supplies and current amplifier are OFF before installing or replacing
the argon tube in the Argon Tube Enclosure
Note: Replace the cables and power cords with the same type.
8 012-14264A
Franck-Hertz Experiment Tunable DC (C onstant Voltage) Power Sup p ly I
Power
Switch
PASCO 850
Universal
Interface
Ports
Power
Switch
PASCO 850
Universal
Interface
Ports
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SE-9639 Franck-Hertz Experiment
Power
Switch
PASCO 850
Universal
Interface
Port
10 012-14264A
Franck-Hertz Experiment Ex periment Procedu r e 1
Experiment Procedure 1
Adjust Operating Voltages
Note: Before switching on the power, be sure that all voltage controls are
turned fully counterclockwise.
1. Connect all the cables and cords as shown in the section “Connect Cables and Cords” (page 7).
3. On the DC Current Amplifier, turn the CURRENT RANGES switch to 10-10 A. To set
the current amplifier to zero, press the SIGNAL button in to CALIBRATION. Adjust NOTE: It is very important to
the CURRENT CALIBRATION knob until the current reads zero. Press the SIGNAL allow the argon tube and
button to MEASURE. apparatus to warm up for 15
minutes prior to making any
4. On the DC (Constant Voltage) Power Supply I, set the Voltage Range switch to -4.5 – measurements.
+30 V. On Power Supply II, set the Voltage Range switch to 0 – 100 V.
5. On Power Supply I, rotate the 0 – 6.3 V adjust knob until the voltmeter reads 3.5 V. This sets VH = 3.5 V (Filament Volt-
age). Note: The Argon Tube Enclosure may have a different suggested filament voltage. If so, use it instead of 3.5 V.
6. On Power Supply I, rotate the -4.5 – +30 V adjust knob until the voltmeter reads 1.5 V. This sets VG1K = 1.5 V (the volt-
age between the first grid and the cathode)
7. Rotate the 0 – 12 V adjust knob until the voltmeter reads 10.0 V to set VG2A = 10.0 V (Retarding voltage).
8. Rotate the 0 – 100 V adjust knob until the voltmeter reads 0 V. This sets VG2K = 0 V (Accelerating voltage).
9. Remember, allow the argon tube and the apparatus to warm up for 15 minutes.
10. When you have finished the above steps, check that VH = 3.5 V (Filament voltage), VG1K = 1.5 V (the voltage between
the first grid and cathode), and VG2A = 10.0 V (voltage between the second grid and anode – “retarding voltage”). If so,
the equipment is ready to do the experiment. Note: These are suggested settings for the experiment, but other values could
be tried. You can do the experiment by parameters that are marked on the Argon Tube Enclosure.
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SE-9639 Franck-Hertz Experiment
Manual Measurements
Note:
• During the experiment, pay attention to the output current ammeter when the voltage is over 60 V. If
the ammeter’s reading increases suddenly, decrease the voltage at once to avoid the damage to the
tube.
• If you want to change the value of VG1K, VG2A and VH during the experiment, rotate the “0 ~ 100 V”
adjust knob fully counter-clockwise before making the changes.
• The filament voltage is tunable from 0 to 6.3V. If the anode output current is too high and causes the
amplifier to overflow, the filament voltage should be decreased.
• As soon as you have finished the experiment, return the VG2A voltage to 0 V to prolong the life of the
argon tube.
1. Increase the accelerating voltage VG2K by a small amount (for example, 1 V). Record the new accelerating voltage VG2K
(value read on voltmeter) and current IA (read on “Ammeter”) in Table 1:1. Continue to increase the voltage by the same
small increment and record the new voltage and current each time in Table 1:1. Stop when the accelerating voltage VG2K
= 85V. (If the current IA exceeds the range, reduce the filament voltage (for example, 0.1V) and start over again.)
2. Try to identify the “peak positions”, i.e. watch for those values of the accelerating voltage VG2K for which the current
reaches a local maximum and begins to drop on further increase of the accelerating voltage. Take a few data points (VG2K,
IA) around these peak positions and record them in Table 1:2. Try to identify the “valley positions”, i.e. watch for those
values of the accelerating voltage VG2K for which the current reaches a local minimum and begins to rise on further
increase of the accelerating voltage. Take a few data points (VG2K, IA) around these valley positions and record them in
Table 1:2.
3. Take sufficiently many voltage values so as to allow you to determine the positions of the peaks and valleys.
VG2K (V)
IA (x 10-10 A)
V1 V2 V3 V4 V5 V6
Analysis
12 012-14264A
Franck-Hertz Experiment Questions
2. Find the peak (or valley) positions which match the accelerating voltages labeled “V1, V2, V3, V4, V5, and V6”.
V2 – V1 + V3 – V2 + V4 – V3 + V5 – V4 + V6 – V5
V 0 = ----------------------------------------------------------------------------------------------------------------------------------------------------
5
5. Calculate the percent difference between the experimental value and the accepted value (h0 =6.626 x 10-34 J•s)
h = | (h - h0) / h0 | x 100% =
Questions
1. Should you use the positions of the peaks or of the valleys to determine the excitation energy? Or both? Explain.
2. Why are the peaks and valleys smeared out rather than sharp?
3. How precisely can you determine the peak/valley position? Explain and justify your estimates.
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SE-9639 Franck-Hertz Experiment
Experiment Procedure 2
Using a PASCO Interface and Data Acquisition Software
Current Amplifier
Interface Port
Argon Tube
Power Supply I Enclosure
Analog Analog
Input A Input B
Items Needed
Item* Quantity
850 Universal Interface (UI-5000) 1
PASCO Capstone Software (UI-5400) 1
Note: Before connecting any cords or cables, be sure that all power switches on the
Interface, Power Supplies, and Current Amplifier are in the OFF position and all volt-
age controls are turned fully counterclockwise.
1. Connect all the cables and cords between the argon tube enclosure and the power supplies and current amplifier.
2. Connect one 8-pin DIN Extension Cable (UI-5218) from the INTERFACE port on the DC Current Amplifier to ANA-
LOG INPUT A on the Universal Interface (UI-5100).
14 012-14264A
Franck-Hertz Experiment Software Setup
3. Connect a second 8-pin DIN Extension Cable from the 0 - 100V / 0 - 200V INTERFACE port on Power Supply II to
ANALOG INPUT B on the Universal Interface.
4. Turn ON the power for the Universal Interface, the power supplies, and the current
amplifier.
5. On the DC Current Amplifier, turn the CURRENT RANGES switch to 10-10 A. To set
the current amplifier to zero, press the SIGNAL button in to CALIBRATION. Adjust
the CURRENT CALIBRATION knob until the current reads zero. Press the SIGNAL NOTE: It is very important to
button to MEASURE. allow the argon tube and
apparatus to warm up for 15
6. On the DC (Constant Voltage) Power Supply I, set the Voltage Range switch to -4.5 – minutes prior to making any
+30 V ( ). On Power Supply II, set the Voltage Range switch to 0 – 100 V ( ). measurements.
7. On Power Supply I, rotate the 0 – 6.3 V adjust knob until the voltmeter reads 3.5 V.
This sets VH = 3.5 V (Filament Voltage). Note: The Argon Tube Enclosure may have a different suggested filament volt-
age. If so, use it instead of 3.5 V.
8. On Power Supply I, rotate the -4.5 – +30 V adjust knob until the voltmeter reads 1.5 V. This sets VG1K = 1.5 V (the volt-
age between the first grid and the cathode)
9. Rotate the 0 – 12 V adjust knob until the voltmeter reads 10.0 V to set VG2A = 10.0 V (Retarding voltage).
10. Rotate the 0 – 100 V adjust knob until the voltmeter reads 0 V. This sets VG2K = 0 V (Accelerating voltage).
11. Remember, allow the argon tube and the apparatus to warm up for 15 minutes.
12. When you have finished the above steps, check that VH = 3.5 V (Filament voltage), VG1K = 1.5 V (the voltage between
the first grid and cathode), and VG2A = 10.0 V (voltage between the second grid and anode – “retarding voltage”). If so,
the equipment is ready for the experiment. Note: These are suggested settings for the experiment, but other values could
be tried. You can do the experiment by parameters that are marked on the Argon Tube Enclosure.
Software Setup
2. The current is a very small number, so to make the current to appear as a number between zero and 100 on the graph, cre-
ate a calculation:
4. Create a digits display of the Voltage. This will clearly show you the accelerating voltage so you can monitor it to make
sure that you do not exceed 85 V.
5. Create a table and create Run-tracked User-Entered Data called Peak Voltage with units of (V).
7. Add a column and create Run-tracked User-Entered Data called Trough Voltage with units of (V).
012-14264A 15
SE-9639 Franck-Hertz Experiment
Recording Data
2. After the filament has warmed up for about 15 minutes, click Record and slowly increase the accelerating voltage (take
about two minutes). Do not exceed 85 V.
CAUTION: While you are increasing the voltage, if you see the current suddenly increase, immediately
return the voltage to zero and decrease the filament voltage slightly, Wait for a few minutes for it to cool,
and repeat the recording.
Analysis
1. Using the coordinates tool on the graph, find the voltage of each of the peaks and troughs and record them in the table in
the Peak Voltage and Trough Voltage columns respectively.
2. The voltage differences between adjacent peaks and the voltage differences between adjacent troughs will be calculated
automatically in the table. Record the mean and standard deviations for the differences. The standard deviations give
the uncertainties in the difference measurements.
3. Use the mean voltage difference (V0) to calculate the value of Planck's Constant, h:
V0
h = e ------
c
where e = 1.602 x 10-19 C, = 108.1 nm and c = 3 x 108 m/s. The answer will be in J•s.
4. Calculate the percent difference between the experimental value and the accepted value (ho = 6.626 x 10-34 J•s).
5. Estimate the uncertainty in the experimental value of Planck's Constant using the uncertainty in the voltage difference.
16 012-14264A
Franck-Hertz Experiment Analysis
012-14264A 17
SE-9639 Franck-Hertz Experiment
Relative humidity: Noncondensing < 10°C, 90% from 10°C to 30°C, 75% from 30°C to 40°C
Pollution degree: 2
Certifications CE
Overvoltage category: II
Item Description
Tunable DC (Constant Voltage) 0~6.3 V DC, I 1A (ripple < 1%), 3.5 Digit Display;
Power Supply I -4.5~0 V DC / -4.5~30 V DC (ripple < 1%) (Two ranges),
I 10mA, 4.5 Digit Display;
Tunable DC (Constant Voltage) 0~12 V DC, I 1A (ripple < 1%), 3.5 Digit Display;
Power Supply II 0~100 V DC / 0~200 V DC (ripple < 1%) (Two ranges),
I 30mA, 3.5 Digit Display
DC Current Amplifier Current range: 10-8~10-13 A, in six ranges, 3.5 Digit Display;
Zero drift ±1% of full range reading in 30 minutes at the
range of 10-13 A (after a 20 minute warm-up)
18 012-14264A
Franck-Hertz Experiment Appe ndix B: Teacher’s Notes
VG2K (V) 1 2 3 4 5 6 7 8 9 10
IA (x 10-10 A) 0 0 0 0 0 0 0 0 0 0
VG2K (V) 11 12 13 14 15 16 17 18 19 20
IA (x 10-10 A) 143 153 153 145 130 118 131 183 270 343
VG2K (V) 31 32 33 34 35 36 37 38 39 40
IA (x 10-10 A) 413 448 441 391 332 243 173 145 220 417
VG2K (V) 41 42 43 44 45 46 47 48 49 50
IA (x 10-10 A) 609 772 825 806 702 547 352 199 113 197
VG2K (V) 51 52 53 54 55 56 57 58 59 60
IA (x 10-10 A) 446 771 1032 1174 1216 1101 883 660 343 167
VG2K (V) 61 62 63 64 65 66 67 68 69 70
IA (x 10-10 A) 118 323 671 1093 1351 1522 1514 1369 1104 756
VG2K (V) 71 72 73 74 75 76 77 78 79 80
IA (x 10-10 A) 468 260 227 456 842 1270 1561 1730 1760 1621
VG2K (V) 81 82 83 84 85
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SE-9639 Franck-Hertz Experiment
V1 V2 V3 V4 V5 V6
Analysis
Obtain the value of argon atom’s first excitation potential (V0):
V0(peak) = (V6- V1)/5 = 11.3 V;
V0(valley) = (V6- V1)/5 = 12.0 V;
Therefore: V0 = 11.65 V;
Calculate the value of Planck’s Constant, h
V0
h = e ------
c
where e = 1.602 x 10-19 C, = 108.1 nm, and c = 3 x 108 m/s. Based on the data, Planck’s Constant, h = 6.725 x 10-34 J•s
Calculate the percent difference between the experimental value and the accepted value (h0 =6.626 x 10-34 J•s)
h = | (h - h0) / h0 | x 100% = 1.5%.
Questions
1. Should you use the positions of the peaks or of the valleys to determine the excitation energy? Or both? Explain.
20 012-14264A
Franck-Hertz Experiment Sample Da ta 2 : U sin g a P ASC O Interface
Use both. The average of the accelerating voltages matching peak positions and the valley positions is the voltage for the
approximate excitation energy, e•U0.
2. Why are the peaks and valleys smeared out rather than sharp?
The shape of the peaks and valleys in the curve is affected by the fact that there is a potential drop of 1.5 V at the cathode,
which is the source of the electrons. The cathode potential causes the peaks and valleys to occur over a space of 1.5 V, rather
than at a sharp point.
3. How precisely can you determine the peak/valley position? Explain and justify your estimates.
Note that the current fluctuations in the vicinity of the peaks, the width of the peaks, the steepness of the drop-off or rise, and
background height and shape all may play a role in this
The molecular contaminant in the tube has a different first excitation potential (V0), so that the measurement of argon atom’s
first excitation potential would be affected.
Sample Data 2: Using a PASCO Interface
Filament voltage (V) = 3.55 V
VG1K = 1.5 V
VG2A = 11.0 V
012-14264A 21
SE-9639 Franck-Hertz Experiment
Analysis
Obtain the value of argon atom’s first excitation potential: V0 = 11.44 V;
Calculate the value of Planck’s Constant, h
V0
h = e ------
c
1. Should you use the positions of the peaks or of the valleys to determine the excitation energy? Or both? Explain.
Use both. The average of the accelerating voltages matching peak positions and the valley positions is the voltage for the
approximate excitation energy, e•U0.
2. Why are the peaks and valleys smeared out rather than sharp?
The shape of the peaks and valleys in the curve is affected by the fact that there is a potential drop of 1.5 V at the cathode,
which is the source of the electrons. The cathode potential causes the peaks and valleys to occur over a space of 1.5 V, rather
than at a sharp point.
3. How precisely can you determine the peak/valley position? Explain and justify your estimates.
Note that the current fluctuations in the vicinity of the peaks, the width of the peaks, the steepness of the drop-off or rise, and
background height and shape all may play a role in this
The molecular contaminant in the tube has a different first excitation potential (V0), so that the measurement of argon atom’s
first excitation potential would be affected.
22 012-14264A
Franck-Hertz Experiment Appe ndix D: Product End of Life
Copyright Notice
The PASCO scientific manual is copyrighted and all rights reserved. However, permission is granted to non-profit educational
institutions for reproduction of any part of the providing the reproductions are used only for their laboratories and are not sold
for profit. Reproduction under any other circumstances, without the written consent of PASCO scientific, is prohibited.
Warranty
For a description of the product warranty, see the PASCO catalog.
012-14264A 23