TOPS Physics
Electronic Trainer
Series and Parallel Capacitors
A capacitor is an electronic component that stores charge. If connected to a voltage source,
charge will flow into a capacitor until the capacitor’s voltage is the same as that of the voltage
source. The measure of capacitance is the amount of charge that is stored for each volt of
potential difference (Coulombs per Volt). In the first part of this lab, we will charge and
discharge a capacitor while recording the voltage across the capacitor and the current going into
the capacitor.
Equipment:
Electronics Trainer
iBook computer
Vernier interface
Multimeter
(2) voltage probes
Component Box
Cautions:
This equipment is delicate. Most of the components are already bent to the correct shapes.
Avoid bending the components if you don’t have to. Do not apply power until you are instructed
to do so!!
Never, never, never short-circuit the power supply! Doing so will (if you are lucky) blow the
fuse. If you’re not lucky, it will blow the whole $200 trainer unit! Don’t plug a wire into the
trainer unless you are told to do so!
Be very cautious when using the meter to read current! If you put more than 200mA through
the meter you will blow a fuse. The meter will have to be disassembled to replace this fuse,
which will not please your teacher in the least! As a rule of thumb, never leave the red lead
plugged into the “µAmA” socket. Always move the red lead to the “VΩ” socket when done
taking a current measurement.
Never apply more than 10V to the Vernier voltage probes. The supply voltage test is critical
to this!
Procedure to test the characteristics of capacitors in series and parallel:
The breadboard is set up with power sockets marked with blue and red lines. The rest of the
breadboard consists of sockets in a grid marked vertically with letters and horizontally with
numbers. Each vertical set of five sockets is connected together within the breadboard. For
example, socket 5a is connected to 5b, 5c, 5d, and 5e, but not to 5f. You will plug components
directly into the breadboard sockets and use jumper wires to connect them together.
You will be setting up a simple series circuit with a capacitor and a resistor in series. You will
attach voltage probes to the capacitor and resistor so that you may monitor the voltage across and
current through the capacitor. After you record data, you will create another circuit with
capacitors in parallel and a third with capacitors in series, recording and comparing data for each..
1. Open the trainer, make sure that the red rocker switch is toward “OFF” and plug the line
cord into a wall outlet.
2. Make sure that both of the knobs on the “POWER SUPPLY” section are turned fully
counterclockwise.
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Note: This circuit will be constructed entirely on the upper breadboard and upper power bus. Do
not put any components on the lower breadboard or the middle or lower power buses.
3. Using a short black jumper, connect one of the GND sockets in the power supply to the
leftmost socket just below the blue line on the upper edge of the upper breadboard. This
will be your negative power bus.
4. Using a short red jumper (a “jumper” is a short piece of wire used to make connections),
connect one of the sockets just below data switch “SW1” to any of the sockets just above
the red line on the upper breadboard. The data switches control a 5V power supply that
connects to the socket below each switch. This will be your positive power bus.
5. Make sure that all of the logic and data switches are in the off (down) position.
6. Locate a 470µF capacitor and insert it sockets 15e and 15f. Make sure that the negative
side of the capacitor (marked with a stripe on the capacitor) is plugged into socket 15e.
7. Locate a 1kΩ resistor and use it to connect socket 45d to socket 45g.
One of the basic realities of life is that resistors seldom have exactly the values they say. That’s
why they have a tolerance band! Now you will use the meter to measure the actual resistance of
the 1kΩ resistor:
8. Plug the socket end (90° bend)of the black test lead into the “COM” terminal of the meter
and the socket end of the red test lead into the “VΩ” terminal of the meter.
9. Turn the meter’s dial to “2K” on the “Ω” scale.”
10. Make sure that the power switch on the trainer is in the “OFF” position. Taking
resistance readings from a powered circuit will ruin the meter! Even though these
resistors aren’t hooked to anything yet, it is good practice to make sure that there is no
chance of accidentally measuring a powered circuit.
11. Touch the meter leads to both sides of the 1kΩ resistor and record the true value here
beneath the nominal value:
Nominal Value
1kΩ
True Value
kΩ
In the next procedure you will check your voltage source. It should be 5V.
12. Plug a medium black jumper into the negative bus socket just to the right of the existing
black jumper.
13. Plug a short red jumper into the positive bus on the right end of the breadboard. (Use the
rightmost socket just above the red line)
14. Turn the meter’s dial to “20” on the “V” scale.
15. Use the red and black wires with alligator clips to connect the red and black meter probes
to the free ends of the red and black jumpers just inserted into the breadboard. Do not let
the black lead touch the red lead!
16. Turn the red rocker switch in the bottom left hand corner of the trainer to “ON.” The
switch illuminates..
17. Flip data switch 1 (SW1) on.
18. Record the true voltage below:
Nominal Value
5V
True Value
V
19. Flip data switch 1 off.
20. Turn the rocker switch off.
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21.
22.
23.
24.
Disconnect the alligator clips from the red and black jumpers and meter leads.
Disconnect the meter leads from the meter and put them away.
Turn the meter knob to “0”.
Plug the free end of the black jumper (coming from the negative bus) into socket 15a. .
You may have to move it closer to row 15.
25. Use a long blue jumper to connect socket 15j to socket 45a.
26. If it isn’t already there, plug a voltage probe into CH 1 of the Vernier interface.
27. Attach the red end of the voltage probe to the capacitor lead that goes into socket 15e.
Push the button on the end of the probe and “hook” the capacitor lead. This will sense the
voltage across the capacitor
28. Attach the black end of the voltage probe to the capacitor lead that goes into socket 15f.
This is the point against which the voltage is referenced.
29. If it isn’t already there, plug a voltage probe into CH 2 of the Vernier interface.
30. Attach the red end of the voltage probe to the resistor lead that goes into socket 45g. This
will be used to sense the voltage across the resistor. The Vernier software will translate
this voltage into a current for display.
31. Leave the black end of the voltage probe unconnected. The other black voltage probe
will provide the voltage reference for both probes.
32. If it hasn’t already been done, plug the USB connector into the iBook and turn the iBook
on. Login as Student, the password is “student”.
33. From the “Student” folder, start the “Lyle’s Cap Lab” item (single click). You might be
asked to clear a couple of “experiment notes” screens. Go ahead and do so.
34. Use the short red jumper currently connected to the right end of the positive bus to
connect socket 45J to any socket on the positive bus. You may have to move it closer to
row 45.
Now you are ready to collect data. You should see a blank graph and a table on the screen. At
the top of the screen is a button labeled “Collect”
35. Turn the rocker switch on.
36. Click on the “Collect” button on the iBook. Nothing will happen, since the software has
been set to start when it detects current in the circuit.
37. Flip data switch “SW1” to the ON (up) position
38. Wait for the data table to appear (in about 5 seconds)
39. After the data appears in the table, flip data switch “SW1” to the OFF (down) position.
40. You should see two nice smooth curves. If not, check your connections, click on the
“Collect” button and try again.
41. On the iBook, Click on “File”
42. Click on “Save As…”
43. Key in your period, group and run numbers and press enter or the “return” key. (example:
period 1, group 4, run 1 would be P1G4R1)Your data is now saved.
44. Answer the following questions (after you’ve collected all your data):
Q#1. Did the capacitor voltage increase or decrease with time?
Q#2. Was the change linear?
Q#3. Did the capacitor current increase or decrease with time?
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Q#4. Was the change linear?
Q#5. How long did it take for the capacitor voltage to reach 5V?
Q#6. The area under the current graph represents the charge stored in the capacitor. Estimate the
stored charge (in µC) by estimating the number of squares under the Capacitor Current curve.
Each square represents 1000µC. Record the value here.
Q#7. The Logger Pro Software will calculate the area under the curve for you by taking the
integral. Click on the analyze menu then on integrate, then choose current. Record the area value
here.
Q#8. The formula for charge stored in a capacitor is q=CV. If C is 470µF and V is 5V, what is
the calculated charge in the capacitor?
Q#9. How do these three values compare?
Now you are going to add another capacitor in parallel with the first one.
45. Take another 470µF capacitor and plug its negative lead into socket 10e.
46. Plug the other lead of the new capacitor into socket 10f.
47. Use two short jumpers to connect socket 10c to 15c, and 10 h to 15h.
Now you are ready to collect data.
48. Click on the “Collect” button on the iBook. The screen clears.
49. Flip data switch “SW1” to the ON (up) position
50. Wait for the data table to appear (in about 5 seconds)
51. Flip data switch “SW1” to the OFF (down) position
52. You should see two nice smooth curves. If not, check your connections, click on the
“Collect” button and try again
53. Save your data as above, but be sure to give this run a different number.
54. Answer the following questions:
Q#10: How long did it take for the capacitor voltage to reach 5V? How does this compare to the
previous trial?
Q#11: The area under the current graph represents the charge stored in the capacitor. Estimate
the stored charge (in µC) by estimating the number of squares under the Capacitor Current curve.
Each square represents 1000µC. Record the value here.
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Q#12: The Logger Pro Software will calculate the area under the curve for you by taking the
integral. Click on the analyze menu then on integrate, then choose current. Record the area value
here.
Q#13: The formula for charge stored in a capacitor is q=CV. If each capacitor is 470µF and V is
5V, what is the calculated charge in the capacitors? Remember that the formula for calculating
net capacitance of the parallel pair is Cparallel=C1+C2.
Q#14: How do these three values compare?
Q#15: Is more charge stored in the two capacitors in parallel than was stored in a single
capacitor?
Now you are going to add another capacitor in series with the first one.
55. Remove the second capacitor from the breadboard.
56. Disconnect the end of the blue jumper that is in socket 15j.
57. Plug the negative lead of the loose 470µF capacitor into socket 15j and the other lead into
socket 18j.
58. Plug the free end of the blue jumper into socket 18h. Now you have a circuit with the two
capacitors in series.
59. Detach the black probe from the capacitor lead going into socket 15f and attach it to the
capacitor lead going into socket 18j
Now you are ready to collect data
60. Click on the “Collect” button on the iBook. The display clears.
61. Flip data switch “SW1” to the ON (up) position
62. Wait for the data table to appear (in about 5 seconds)
63. Flip data switch “SW1” to the OFF (down) position
64. You should see two nice smooth curves. If not, check your connections, click on the
“Collect” button and try again
65. Save your data as above, again with a different run number.
66. Answer the following questions:
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Q#16: How long did it take for the capacitor voltage to reach 5V?
Q#17: The area under the current graph represents the charge stored in the capacitor. Estimate
the stored charge (in µC) by estimating the number of squares under the Capacitor Current curve.
Each square represents 1000µC. Record the value here.
Q#18: The Logger Pro Software will calculate the area under the curve for you by taking the
integral. Click on the analyze menu then on integrate, then choose current. Record the area value
here.
Q#19: The formula for charge stored in a capacitor is q=CV. If each capacitor is 470µF and V is
5V, what is the calculated charge in the capacitors? Remember that the formula for calculating
net capacitance of the series pair is 1/Cseries=1/C1+1/C2.
Q#20: How do these three values compare?
Q#21: Is more charge stored in the two capacitors in series than was stored in a single capacitor?
67.
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71.
72.
Click on “Data”
Click on “Clear All Data”
Click on the “Yes” button.
Quit the program, go to the file menu and select quit. When asked do not save data.
Logout of the computer, go to the special menu and select logout.
Remove all components from the breadboard and return the trainer to the condition in
which you found it. You may leave the Vernier interface and probes set up.
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Teacher Reference
Introduction:
In this exercise, students use data collection equipment to determine voltage and current
curves of a capacitor, two capacitors in parallel, and two capacitors in series. They will
compute the both the theoretical and actual charge stored in the capacitors.
Experimental goals:
After completing this experiment, students will be able to collect current and voltage data
from a charging capacitor. They will be able to predict whether a single capacitor, two
capacitors in parallel, or two capacitors in series will store more charge for a given voltage.
Equipment:
Electronics Trainer
Vernier interface
(2) voltage probes
iBook computer
Multimeter
Component Box
Keywords:
Capacitance, Voltage, Current, Parallel Circuits, Series Circuits.
Notes:
No particular cautions with this lab. If things aren’t working right, have the other lab partner
check the circuit step-by-step.
If the voltage and current reading are fluctuating, try wiggling the components and jumpers to
make better contact with the breadboard.
The calculated values for stored charge should be close to the “counting squares” values, but
keep in mind that the “counting squares” process is rather inaccurate.
ANSWER KEY:
*Characteristics of a single capacitor*
1. In general, capacitors in parallel will store more charge then single capacitors, while
capacitors in series will store less charge than single capacitors. Capacitor voltage should
increase with time until the capacitor is “filled”.
2. None of the curves should be linear.
3. Capacitor current decreases with time. As charge is stored, it becomes harder and harder to
add more like charges to a plate.
4. No, the change is not linear.
5, 6, and 7. Student answers will vary.
8. q=470µF(5V) = 2350µC
9. Measured values may be slightly different than theoretical values; measured values will
depend on the voltage and resistance of each set of equipment.
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*Two capacitors in parallel*
10. It should take longer for capacitors in parallel to reach 5V than it takes a single capacitor
to reach 5V. Thus, the parallel run is slower than the first run.
11, 12. Student answers will vary.
13. q=4700µC
14. Actual values should be close to theoretical values, but may vary depending on
experimental set-up and methods.
15. Yes, approximately twice as much charge is stored in two capacitors in parallel than in a
single capacitor.
*Two capacitors in series*
16, 17, 18. Student answers will vary.
19. q=1175µC
20. Actual values may vary from theoretical values, but ideally they would be within 10%
accuracy.
21. Two capacitors in series do not store more charge than a single capacitor.
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