Download Series and Parallel circuits

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Series and Parallel circuits
Components in an electrical circuit are in series when they are connected one after the
other, so that the same current flows through both of them. Components are in parallel
when they are in alternate branches of a circuit. Series and parallel circuits function
differently. You may have noticed the differences in electrical circuits you use. When
using some decorative holiday light circuits, if one lamp burns out, the whole string of
lamps goes off. These lamps are in series. When a light bulb burns out in your house, the
other lights stay on. Household wiring is normally in parallel.
Series Resistors
Parallel Resistors
You can monitor these circuits using a Current Probe and a Voltage Probe and see how
they operate. One goal of this experiment is to study circuits made up of two resistors in
series or parallel. You can then use Ohm’s law to determine the equivalent resistance of
the two resistors.
STUDENT OUTCOMES
Through this experiment, students will learn:
- How the current flow in series and parallel circuits
- Voltage differences in series and parallel circuits
- Ohm’s law
MATERIALS
Tablet PC Computer Laptop
Logger Pro
Vernier Current Probe
Vernier Differential Voltage Probe
Vernier Computer Interface
Vernier Circuit Board
Power Supply
Wires
PRELIMINARY SETUP AND QUESTIONS:
1. Connect the following circuit in series and watch the intensity of the
light bulb. Use R1=10Ω and R2=10Ω for both resistors.
2. Reconnect the above circuit, disconnect R2 so that only R1 is
present. What happened to the light bulb intensity?
3. If there is a correlation between the light bulb intensity and the
amount of current running through the bulb, write down a
mathematical relationship between the Intensity running through this
one-loop circuit (series) and the resistance. To help you figure out this
relationship, fill out the blanks:
I: current / R: resistance
As I increases, R …….
As I decreases, R …….
Therefore the relation between I and R is:
(write down the mathematical relationship)
4. Are you able to relate this relationship to any law you might know
of? If so, state it.
5. Connect the following circuit in parallel and watch the intensity of
the light bulb. Use R1=10Ω and R2=10Ω for both resistors.
6. Is the intensity of the light bulb higher or lower than when the
circuit was in series?
7. Using the relationship obtained in 4. what does this mean
concerning the current running through the light bulb? Is it higher or
lower than in series?
8. Imagine that the flow of electron running through a circuit can be
modeled by a flow of Water running through pipes. Using arrows, show
on both diagram above, how the current flows and the path it uses.
9. Obviously, the current flows through both resistors in the series and
the parallel circuit. If we assume a direct relationship between the
number of electrons flowing through a circuit and the current in that
circuit, answer the following: in the parallel circuit, if we assume
conservation of electrons (charge) the number of electron arriving at
point B must be the same as the number of electrons reaching point A.
Hence, if n electrons arrive at point B and R1=R2, what is the number
of electrons flowing through each branch if n electrons arrive at point
A?
10. Assuming the Voltage stays the same, if R1 is doubled (meaning
the resistance to current through this branch is double), do you expect
the number of electron to flow through this branch to be lower or
higher? Write down the relationship between I1 and I2 when R1=R2
and then R1=2R2.
PROCEDURE:
Part I Series circuits
1.Connect the Current Probe to Channel 1 and the Differential Voltage
Probe to Channel 2 of the interface.
2.Open the file “26a Series Parallel Circ” in the Physics with Computers
folder. Current and voltage readings will be displayed in a meter.
3.Connect together the two voltage leads (red and black) of the
Voltage Probe. Click
, then click
to zero both sensors. This
sets the zero for both probes with no current flowing and with no
voltage applied.
4. Connect the series circuit shown in Figure 2 using the 10  resistors
for resistor 1 and resistor 2. Notice the Voltage Probe is used to
measure the voltage applied to both resistors. The red terminal of the
Current Probe should be toward the + terminal of the power supply.
5.For this part of the experiment, you do not even have to click on the
button. You can take readings from the meter at any time. To
test your circuit, briefly press on the switch to complete the circuit.
Both current and voltage readings should increase. If they do not,
recheck your circuit.
6.Press on the switch to complete the circuit again and read the
current (I) and total voltage (VTOT). Record the values in the data
table.
7.Connect the leads of the Voltage Probe across resistor 1. Press on
the switch to complete the circuit and read this voltage (V1). Record
this value in the data table.
8.Connect the leads of the Voltage Probe across resistor 2. Press on
the switch to complete the circuit and read this voltage (V2). Record
this value in the data table.
9.Repeat Steps 5 – 8 with a 50  resistor substituted for resistor 2.
10. Repeat Steps 5 – 8 with a 50  resistor used for both resistor 1
and resistor 2.
Part II Parallel circuits
11. Connect the parallel circuit shown below using 50  resistors for
both resistor 1 and resistor 2. As in the previous circuit, the Voltage
Probe is used to measure the voltage applied to both resistors. The red
terminal of the Current Probe should be toward the + terminal of the
power supply. The Current Probe is used to measure the total current
in the circuit.
+
-
R1
I
Red
R2
Black
Figure 3
12. As in Part I, you can take readings from the meter at any time.
To test your circuit, briefly press on the switch to complete the circuit.
Both current and voltage readings should increase. If they do not,
recheck your circuit.
13. Press the switch to complete the circuit again and read the total
current (I) and total voltage (VTOT). Record the values in the data
table.
14. Connect the leads of the Voltage Probe across resistor 1. Press
on the switch to complete the circuit and read the voltage (V1) across
resistor 1. Record this value in the data table.
15. Connect the leads of the Voltage Probe across resistor 2. Press
on the switch to complete the circuit and read the voltage (V2) across
resistor 2. Record this value in the data table.
16. Repeat Steps 13 – 15 with a 68  resistor substituted for
resistor 2.
17. Repeat Steps 13 – 15 with a 68  resistor used for both resistor
1 and resistor 2.
Part III Series and Parallel circuits
18. Connect the parallel circuit shown below using 50  resistors for
resistor 1, 10  resistors for resistor 2 and 68  resistors for resistor
3. As in the previous circuit, the Voltage Probe is used to measure the
voltage applied to both resistors. The red terminal of the Current Probe
should be toward the + terminal of the power supply. The Current
Probe is used to measure the total current in the circuit.
Figure 3
19. As in Part I, you can take readings from the meter at any time. To
test your circuit, briefly press on the switch to complete the circuit.
Both current and voltage readings should increase. If they do not,
recheck your circuit.
20. Press the switch to complete the circuit again and read the total
current (I) and total voltage (VTOT). Record the values in the data
table.
21. Connect the leads of the Voltage Probe across resistor 1. Press on
the switch to complete the circuit and read the voltage (V1) across
resistor 1. Record this value in the data table.
22. Connect the leads of the Voltage Probe across resistor 2. Press on
the switch to complete the circuit and read the voltage (V2) across
resistor 2. Record this value in the data table.
23. Connect the leads of the Voltage Probe across resistor 3. Press on
the switch to complete the circuit and read the voltage (V3) across
resistor 3. Record this value in the data table.
DATA TABLE
Part I: Series circuits
R1
()
R2
()
1
10
10
2
10
50
3
50
50
I
(A)
V1
(V)
V2
(V)
Req
()
VTOT
(V)
V2
(V)
Req
()
VTOT
(V)
Part II: Parallel circuits
R1
()
R2
()
1
50
50
2
50
68
3
68
68
I
(A)
V1
(V)
Part III: Series and Parallel
I
(A)
V1
(V)
V2
(V)
V3
(V)
ANALYSIS
Part I
1. Using Ohm’s law, calculate the current running through resistor1.
2. Using Ohm’s law, calculate the current running through resistor2.
3. Recall the assumption made in the preliminary questions concerning
conservation of electrons (current running through a circuit), what
relationship do you expect to find between I, I1, and I2?
4. Calculate V1 + V2 and compute the percent error with Vtotal
(accepted value) measured from your table. Discuss the systematic
errors.
5. Do you have the same relationship as with voltage between I1 and
I2?
6. What can you state concerning the current of two resistors
connected in series?
7. What can you state concerning the voltage of two resistors
connected in series?
8. Calculate the equivalent resistor in this circuit (Table)
Part II
9. Using Ohm’s law, calculate the current running through resistor1.
10. Using Ohm’s law, calculate the current running through resistor2.
11. Recall the assumption made in the preliminary questions
concerning conservation of electrons (current running through a
circuit), what relationship do you expect to find between I, I1, and I2?
12. Calculate I1 + I2 and compute the percent error with I (accepted
value) measured from your table. Discuss the systematic errors.
13. Do you have the same relationship as with current between V1 and
V2?
14. What can you state concerning the current of two resistors
connected in parallel?
15. What can you state concerning the voltage of two resistors
connected in parallel?
16. Calculate the equivalent resistor in this circuit (Table)
Part III
17. Calculate the equivalent resistor for this circuit.
18. Calculate the current I3.
19. Calculate the current I2
20. Calculate the current I1
21. What is the relationship between I3 and Itotal? Is this what you
expect? (Justify)
22. What is the relationship between I1, I2, and I3. Using your
analysis for part II, does this relationship follow your prediction on
14.? If not, explain the discrepancy.