Download Series-Parallel Circuits

Series-Parallel Circuits
OBJECTIVE: To verify the current, voltage, and resistance characteristics of series,
parallel, and series-parallel circuits.
Part I: Resistance Measurement
In this part of the experiment, you will learn to use the resistance color-code, learn to
measure resistance using an ohmmeter, and learn how to build simple series and parallel
resistor arrangements.
A. Using the resistance color-code sheet given below:
Locate the following resistors (circle the ones you use):
R1 = 220  

R2 = 470 or 270  
R3 = 2200 
R4 = 10000 


What is the color code for each of these?
R1 ______________________
R3 ______________________
R2 ______________________
R4 ______________________
According to the color code, what is the tolerance of the resistors used in this
experiment? ______________________
B. Using the ohmmeter, measure the resistance of each of the above resistors. Be sure
you understand how your meter operates.
Measured Resistances:
R1 ______________________
R3 ______________________
R2 ______________________
R4 ______________________
Are the values you measured within the allowed tolerance range? __________
C. Set up the circuit diagrammed below. Do not use wires to connect the resistors. Use
the internal wiring of the bread boarding.
R1
R2
R4
R3
Is this a series or parallel arrangement? ______________________________
Measure the total resistance across the circuit: _______________ 
Based on your measured resistance value for each individual resistor (Part B), calculate
what the equivalent resistance should be for this type of circuit and calculate the percent
error (be sure to show all of your work).
Calculated R = _____________ 
% Error = _________________
D. Using the same four resistors, set up the following circuit. Once again, use the
internal bread board wiring to connect the resistors.
R1
R2
R3
Is this a series or a parallel arrangement? _______________________
Measure the total resistance across the circuit: _______________ 
R4
Calculate what the equivalent resistance should be for this type of circuit and calculate
the percent error (be sure to show all of your work).
Calculated R = _____________ 
% Error = _________________
E. What errors could account for the calculated % errors?
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
Part II: Current Measurement (Series Circuit)
In this part of the experiment, you will learn to measure the current in a DC circuit using
an ammeter.
A. Set up the circuit diagrammed below. Adjust the terminal voltage of the source until
your voltmeter reads 6.0 V (to measure terminal voltage, the source must be connected to
the circuit while the measurement is being made.) Note that these resistors are
different from the ones used in Part I. Circle the ones you use.
R1


6V
R2


  

R1 = 2000
R2 = 470 or 270 
R3 = 150  or 100 
R3
B. Measure the current at several points in the circuit. Remember that the ammeter must
be connected in series with the circuit (you will need to disconnect one of the leads of a
resistor in order to insert the meter in the circuit). Also remember that the positive (red)
meter lead should be connected to the most positive part of the circuit being considered
(otherwise, a negative current will be displayed).
I (current) between voltage source and R1 = _____________ A
I between R1 and R2 = ________________ A
I between R2 and R3 = ________________ A
Average I = _______________ A
What can you conclude about the current in a series circuit from this?
______________________________________________________________________
C. Based on the coded resistance values, calculate what current should be in the circuit
and find the % error with the average measured current. Be sure to show all of your
work.
Calculated I = ______________ A
% Error = _______________ %
Give some reasons for your calculated % error (at least one of these should be different
from those mentioned in Part I).
________________________________________________________________________
________________________________________________________________________
Part III: Current Measurement (Parallel Circuit)
In this part of the experiment, you will investigate the current characteristics of a parallel
circuit.
A. Set up the circuit diagrammed below, using the same resistors as for Part II. Circle
the ones you use. Adjust the terminal voltage of the source until your voltmeter reads
6.0 V (to measure terminal voltage, the source must be connected across the load
resistors while the measurement is being made.)
6V
R1 = 2000 
R2 = 470 or 270 
R3 = 150  or 100 
R1
R2
R3
B. Measure the following currents in the circuit:
I through R1 = ______________ A
I through R2 = ______________ A
I through R3 = ______________ A
C. What does the sum of the currents through the three resistors equal? __________ A
Using the coded resistances for the resistors, calculate what the total current drawn from
the source should be (show work). _____________ A
% Error = ______________ %
D. In summary, current in a series circuit is ____________ throughout, whereas the
__________ of the currents in the branches of a parallel circuit equals the source current.
Please have your instructor initial here ______ before proceeding.
Part IV: Voltage Measurement (Series Circuit)
In this part of the experiment, you will learn how to measure voltages in a DC circuit
using a voltmeter.
A. Using the same circuit as in Part II, measure the voltage across each resistor in the
circuit. Remember that the voltmeter must be connected in parallel with the circuit
element in consideration. Also, as in measuring the current in Part II, be sure to observe
the proper meter polarity.
V across R1 = _______________ V
V across R2 = _______________ V
V across R3 = _______________ V
B. What does the sum of the voltages across the three resistors equal? ____________ V
What do you think it should it equal? _______________ V
What can you conclude about the voltages across the circuit elements in a series circuit?
_______________________________________________________________________
C. Calculate what the voltage should be across each resistor (based on the coded
resistance values and the current calculated in Part II). Find the % error with each
measured value. Be sure to show all of your work.
R1 :
R2 :
R3 :
Calculated V _____________ V
Calculated V _____________ V
Calculated V _____________ V
%Error _____________ %
%Error _____________ %
%Error _____________ %
D. Give some reasons for the % errors.
_____________________________________________________________________
E. In summary, current in a series circuit is _______________ throughout, whereas the
voltage drops across the components _____________ to yield the source voltage.
Part V: Voltage Measurement (Parallel Circuit)
A. Using the same circuit as in Part III, measure the following voltages in the circuit:
V across source = ______________ V
V across R1 = ______________ V
V across R2 = ______________ V
V across R3 = ______________ V
What can you conclude about the voltage in a parallel circuit from this?
___________________________________________________________________
B. In summary, voltage in a parallel circuit is ____________ throughout, whereas the
__________ of the voltages across the resistors in a series circuit equals the source
voltage.
Part VI: Series-Parallel Circuit
In this part of the experiment, you will measure resistance, current, and voltage in a
series-parallel circuit.
A. Using the same resistors as in Parts II, III, and IV, set up the circuit diagrammed
below. Circle the resistors you use.
R1
6V
R2
R3
R1 = 2000 
R2 = 470 or 270 
R3 = 150  or 100 
B. Measure the voltage drop across each resistor and the current through each resistor.
Using these values and Ohm’s law, calculate the resistance of each resistor (show work).
V1 = ______________V
I1 = ______________ A
R1 = ______________ 
V2 = ______________V
I2 = ______________ A
R2 = ______________ 
V3 = ______________V
I3 = ______________ A
R3 = ______________ 

C. Find the % error of each of the calculated resistances in Part B. Compare with the
coded values.
R1: % Error = ____________ %
R2: % Error = ____________ %
R3: % Error = ____________ %
D. How did V2 compare with V3? ______________________________________
What can you conclude about a series-parallel circuit from this?
____________________________________________________________________
E. How did I1 compare with the sum of I2 and I3?
____________________________________________________________________
What can you conclude about a series-parallel circuit from this?
Part VII: Application (Light Bulbs)
A. Using only a AA cell, a mini light bulb, and a single piece of wire, connect a
circuit to light the bulb. Once you are successful, devise three other ways to use
the same apparatus to light the bulb. Demonstrate this to your instructor and have
him/her initial here: __________
B. Make sure that the voltage control knob on the lab table power supply is turned all
the way down (counter-clockwise). Connect a wire (banana plug end) to the
positive (top, red) terminal of the DC supply. Place mini light bulb in a socket.
Connect the other end of the wire coming from the power supply (alligator plug
end) to one of the light bulb socket wires.
C. Repeat step B for a wire connecting the negative (top, black) terminal of the
power supply to the other light bulb socket wire.
D. Connect banana plug wires from the “COM” and “V” terminals of the digital
multi-meter directly to the power supply terminals (“COM” to negative and
“V” to positive). You will need to “piggyback” the banana clips.
E. Set the digital multi-meter to read DC voltage. Make sure the power supply is
turned on, and gradually increase the voltage until the meter reads 2.8 V. The
bulb should be brightly lit at this time. At no time should the voltage across a
single bulb ever exceed 3.5 V!
F. Make note of the brightness of the bulb. Predict what will happen to the total
resistance in the circuit if a second, identical bulb is connected in series with this
bulb (be specific). ______________ What effect will this have on the current in
the circuit? ________________ What effect will this have on the brightness of
the two bulbs in series compared to that for the single bulb?
__________________
G. Place a second light bulb socket in series with the first light bulb. To do this, use
a single alligator clip to connect the two bulbs together, as shown below. Adjust
the voltage back to 2.8 V (if necessary).
Were your predictions upheld? _______________
Predict what you believe will happen for three bulbs connected in series. Be sure
to explain your reasoning.
__________________________________________________________________
_________________________________________________________________
H. Repeat step G for three bulbs in series. Don’t forget to adjust the voltage back to
2.8 V, if necessary.
Were your predictions upheld? ______________
What do you think will happen if you unscrew one of the light bulbs from its
socket? ______________________________________________________
Try unscrewing any one of the three bulbs. Were your predictions upheld?
Explain why this happens.
__________________________________________________________________
__________________________________________________________________
I. Turn the voltage control knob all of the way down. Place a single light bulb in the
circuit and gradually increase the voltage to 2.8 V.
J. Make note of the brightness of the bulb. Predict what will happen to the total
resistance in the circuit if a second, identical bulb is connected in parallel with
this bulb (be specific). ______________ What effect will this have on the total
current flowing from the power supply? ________________ What effect will
this have on the current flowing through the original bulb? _________________
What effect will this have on the brightness of each of the two bulbs in parallel
compared to that for the single bulb? __________________
K. Place a second light bulb in parallel with the first light bulb. To do this, use the
alligator clips from the power supply to connect to both bulbs, as shown below.
Adjust the voltage back to 2.8 V (if necessary).
Were your predictions upheld? If not, explain what was different and why.
__________________________________________________________________
_________________________________________________________________
Predict what you believe will happen for three bulbs connected in parallel. Be
sure to explain your reasoning.
__________________________________________________________________
_________________________________________________________________
L. Repeat step K for three bulbs in parallel. Don’t forget to adjust the voltage back
to 2.8 V, if necessary.
Were your predictions upheld? ______________
What do you think will happen if you unscrew one of the light bulbs from its
socket? ______________________________________________________
Try unscrewing any one of the three bulbs. Were your predictions upheld?
Explain why this happens.
__________________________________________________________________
__________________________________________________________________
M. Turn the voltage control knob all of the way down. Build a circuit consisting of
two light bulbs in series connected to the power supply and gradually increase the
voltage to 3.5 V.
N. Suppose the two original bulbs (A and B in the bottom, left circuit) are now
connected in the circuit below with a third identical bulb (C) in parallel with B
(bottom, right circuit).
A
B
C
Predict what will happen to the brightness of bulb A: __________________
Predict what will happen to the brightness of bulb B: __________________
O. Connect a third bulb in parallel with bulb B to check your predictions (adjust the
voltage back to 3.5 V if necessary). Explain your results to your instructor and
have him/her initial here before proceeding. ________
P. Suppose a wire is connected in parallel with bulbs B and C, as shown below:
Predict what happens to the brightness of bulb A: __________________
Predict what happens to the brightness of bulb B: __________________
Predict what happens to the brightness of bulb C: __________________
Connect a wire in parallel with bulb C to check your predictions (adjust the
voltage back to 3.5 V if necessary). Explain your results to your instructor and
have him/her initial here before proceeding. ________
Q. Suppose two of the light bulbs you used actually had slightly different resistances.
If the two bulbs were connected in parallel with the power supply, what would
you expect to see and why?
__________________________________________________________________
__________________________________________________________________