GWU SEAS ECE Department ©2010
Page
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ECE
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Exper
iment:
DC Circuits: Ohm's Law, Series and Parallel Circuits
The George Washington University
School of Engineering and Applied Science
Department of Electrical
and Computer Engineering
ECE
2
11
0

LAB
Experiment
:
DC Circuits: Ohm's Law,
Series and Parallel Circuits
Equipment:
Lab Equipment
Equipment Description
(1
Set
) Digital Multimeter (DMM)
Keithley Model 175
Digital Multimeter
(DMM)
(2
Pairs
) Test Leads
Banana to mini

grabber test leads
(1 Set) Bread Board
Prototype Bread Board
(1 Set) DC Power Supply
Agilent E3631A
Triple Output DC Power Supply
Table
A
–
Equipment List
Components
:
Kit Part #
Spice Part
Name
Part Description
Symbol Name
(used in schematics
throughout this lab manual)
Resistor
R1
R
750
Ω Resistor
o
1
剥ois瑯爠
刲
o
ㄮ1
h
Ω Resistor
o
2
剥ois瑯爠
刳
o
P
h
Ω Resistor
o
P
Table
B
–
Components List
Objectives
:
To understand
DC series, parallel
,
and series

parallel combination circuit.
To c
onnect electronic
devices
on
a
bread
board.
To
calculate
DC
voltage
across resistors in a
DC series circuit
.
To measure DC voltage across resistors in a DC series circuit using
a
DMM
.
To calculate DC
current through
resistors in a DC parallel circuit.
To measure DC
current through
resistors in a DC parallel circuit using
a
DMM.
To calculate DC current through resistors in a DC series

parallel combination circuit.
To measure DC current through resistors in a DC series

parallel combination circuit using
a DMM.
To c
alculate the total power dissipated by each resistor in a DC
series
,
parallel
, and
series

parallel
combination
circuit
.
GWU SEAS ECE Department ©2010
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Exper
iment:
DC Circuits: Ohm's Law, Series and Parallel Circuits
Prelab
Part 1:
Figure 1
–
䑃⁓er楥猠䍩rcu楴
Figure 2
–
䑃DPar慬a敬e䍩r捵楴
Problem #1
–
DC
Series Circuit
Figure #1
shows a
DC circuit that has two resistors R1 and R2 connected in series with a
DC
Voltage Source (The
label
for the voltage source is VS1).
Circuit Analysis using Ohm's Law
Analyze the circuit in Figure #1.
Use VS1=9Vdc.
Find the nominal (expected) values for
the DC voltage, DC current and Power Consumption of R1 and R2. Show your steps of
calculations clearly and write down your calculated results in Table 1
(see the lab section
below for table 1)
.
Problem #2

DC
Parallel Circuit
Figure 2 shows a
DC circu
it that has tw
o resistors R2 and R3
connected in
parallel
with a
DC
Voltage Source (The
label
for the voltage source is VS2).
Circuit Analysis using Ohm's Law
Analyze the circuit in Figure #2.
Use VS2=9Vdc.
Find the nominal (expected) values for
the
DC Voltage, DC Current and Power Consumption of R2 and R3. Show your steps of
calculations clearly and write down your calculated results in Table 2
(see the lab section
below for table 2).
A
●
B
●
C
●
GWU SEAS ECE Department ©2010
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Exper
iment:
DC Circuits: Ohm's Law, Series and Parallel Circuits
Problem
#3
–
DC Series

Parallel Combination Circuit
Figure 3
–
DC Series
–
Parallel Combination Circuit
Many circuits have a combination of series and parallel resistors.
Figure #3
shows a DC circuit
that has tw
o resistors R2 and R3
connected in
parallel
with one another. R2 and R3 together are
connected
in series with
resistor R1
and
with
the
DC Voltage Source (The
label
for the voltage
source is VS3).
Circuit Analysis using Ohm's Law
Analyze the circuit in Figure #3.
Use VS3=9Vdc.
Find the nominal (expected) values for
the DC Voltage, DC Current and
Power Consumption of R1, R2 and R3. Show your
steps of calculations clearly and write down your calculated results in Table 3
(see the lab
section below for table 3).
GWU SEAS ECE Department ©2010
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Exper
iment:
DC Circuits: Ohm's Law, Series and Parallel Circuits
Prelab
Part
2
:
During the
lab, you will build the three circuits you have analyzed
in part 1 of the prelab
. You will
then measure the voltage
across
and
the
current
through each resistor
to
see if lines up with your
calculated values.
In order to make the measurements it is essential that you know how to hook
up the measurement equipment to the circuits you will build.
In this part of the prelab, instructions on how to measure voltage and current are discussed at a
high level. You w
ill be expected to know this and will potentially be quizzed on this knowledge at
the beginning of lab.
A.
HOW TO MEAURE VOLTAGE ACROSS A RESISTOR:
A Digital Multimeter (DMM) is a
multi

use
measurement device we use in the lab to measure
resistance, voltage
, and current. You used a DMM in lab 1 to measure the resistance of a
resistor. In this lab you will use the DMM to measure voltage.
Voltage is measured “across” an electrical device. In prelab part 1, figure #1 shows two resistors.
After building t
he circuit on a breadboard, if we wish to measure the voltage across resistor R1,
we would do the following using the DMM:
1)
Set the DMM to measure
Voltage
by pressing “V” on the DMM front panel
2)
Set the meter to the
range
we expect the
voltage
to be: (
u
V, m
V
, etc.)
3)
Attach
the two leads/wires coming from the DMM to points A and B in figure #1
a.
In this way, the DMM is “
ACROSS
” R1
4)
Read the value of the voltage measured on the DMM
These are the four conceptual steps to measuring voltage. During lab, the exact procedure will
be demonstrated and explained. But it is expected that be familiar with these conceptual steps
prior to the lab. Questions like, “how does one measure the vol
tage across R2” may appear on a
prelab quiz. If you do not understand these steps, be certain to discuss this with your GTA prior
to lab.
GWU SEAS ECE Department ©2010
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Exper
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DC Circuits: Ohm's Law, Series and Parallel Circuits
B.
HOW TO MEAURE CURRENT THROUGH A RESISTOR:
Current is measured “through” an electrical device
and is done very dif
ferent compared to
measuring voltage
. In prelab part 1, figure #1 shows two resistors. After building the circuit on a
breadboard, if we wish to measure the current through resistor R1, we need to BREAK the circuit
where we wish to measure the current.
We would do the following using the DMM:
1)
Set the DMM to measure
Current
by pressing “A” on the DMM front panel
(A is for AMPS)
2)
Set the meter to the
range
we expect the current to be: (uA, mA, etc.)
3)
Break the circuit where we wish to measure the current
a.
I
n figure #1, we would disconnect
/break
the circuit at point B
b.
Then we can place the two leads/wires of the DMM at the breakpoint as shown in
figure #3
i.
The DMM is now in series with the circuit. Because it is series, we know
the current will be the same
as it will be through R1 and R2.
c.
Now the current will travel from the circuit, THROUGH the DMM, and back to the
circuit
4)
Read the value of the current traveling through the DMM
a.
This is the value of the current in the series circuit
Figure 4
–
DC Series Circuit
w/DMM inserted
Prelab
Problem #4
: Draw the circuit in figure #3. Show how you would attach the DMM to
measure the voltage across R3.
Current
A
●
●
B
C
●
●
B
䑍a
(“A”
–
䵯摥)
GWU SEAS ECE Department ©2010
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DC Circuits: Ohm's Law, Series and Parallel Circuits
L
ab
:
Part
1
–
DC
Series
Circuit
Measurements
1)
Construct the circuit of
Fi
gure #1
–
DC
S
eries Circuit
using your
breadboard.
2)
Use the
Agilent E3631A Triple Output DC Power Supply
as VS
1 and set the voltage to
9
Vdc
using the following procedure:
a.
Do not yet connect the
Agilent
power supply to your circuit!
b.
P
ress the
Power Button
to turn it on.
c.
Press
Output On/Off
once to turn on the output.
d.
Press the
+25V
button to tell the power supply that we want to alter the output
from the
25
V terminals.
e.
Use the
dial
to
change
the display v
alue to
9 volts
.
Note: You can safely ignore
the value of the right most digit for this experiment.
f.
Once you have reached 9
V, Press
Output On/Off
once to turn the output OFF
while you hook up the circuit.
g.
Plug the ‘banana’ end of your cables into the
25
V t
erminals of your power supply
.
h.
Attaching the mini

grabber ends to your circuit
i.
C
heck whether your circuit configuration is correct or not!
j.
If your circuit configuration is correct, p
ress the
Output On/Off
to apply
9 Volts to
your circuit.
3)
Use the DMM (
Keithley Model175) to measure the
DC voltage
across
R1 and R2
and
record it in table 1 using the following procedure:
a.
Switch on the Keithley 175 DMM.
b.
Be sure the AC

DC button is unselected (DC is implied by absence of AC label).
c.
Measure DC voltage by pres
sing the V button.
d.
Select the appropriate voltage range by pressing one of the range buttons or
enable “Auto Range” in order to get the maximum number of significant digits
during
measurement
e.
Connect the DMM into your circuit.
Make sure the DMM is connecte
d
in
parallel with the resistor across which you are going to measure the
voltage!
f.
Record the voltage (value and corresponding units) from the LCD screen
4)
Use the DMM (Keithley Model175) to measure the DC current through R1 and R2 and
record it in table 1.
a.
Measure DC current by pressing the A button.
b.
Select the appropriate current range by pressing one of the range buttons
c.
There is no auto

range for current, you must set it to the range from your
calculations
d.
Break your circuit at the point you wish to meas
ure current.
Connect the DMM
in series with your circuit as discussed in the prelab.
e.
Record the current (value and corresponding units) from the LCD screen
5)
Calculate
the
p
ower c
onsumption of R
1
and R
2
from the measure
d DC
v
oltage and DC
c
urrent of R
1
and R
2
and record it in table 1.
GWU SEAS ECE Department ©2010
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Exper
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DC Circuits: Ohm's Law, Series and Parallel Circuits
Circuit
Simulations in PSPICE
Simulate the circuit in Figure 1 using PSPICE (GTA will show you how to configure it in
PSPICE step by step). Find the simulated voltage, current and power consumption of
each resistor
using the voltage, current and power probes respectively in PSPICE.
Record
your
simulated
results in Table 1
.
Data Analysis
Analyze and interpret Table 1. Include the answers to the following questions when you
are analyzing data:
What is the total voltag
e across R1 and R2? Is it equal to the DC source
voltage VS1? If it is (not), why?
What are the currents flowing through R1 and R2? Are they equal? If they
are (not), why?
Resistors
Electrical Quantities
(units)
R1
R2
Calculated Nominal
Results
Voltage
(V)
Current
(mA)
Power
(mW)
Measured
Results
Voltage
(V)
Current
(mA)
Power
(mW)
Simulated
Results
in PSPICE
Voltage
(V)
Current
(mA)
Power
(mW)
Table
1
–
DC
Series C
ircuit Data
Table
GWU SEAS ECE Department ©2010
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Exper
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DC Circuits: Ohm's Law, Series and Parallel Circuits
Part
2

DC
Parallel Circui
t Measurements
Construct the circuit of Figure #
2
using your breadboard.
Use the
Agilent E3631A Triple Output DC Power Supply
as VS
2
and set the voltage
to
9
Vdc.
Use the procedure you followed in part 1 to set VS2.
Use
the DMM (Keithley Model175) to measure the DC Voltage and DC Current of R
2
and R
3
.
Find the measured Power Consumption of R
2
and R
3
from the measured DC
Voltage and DC Current of R
2
and R
3
.
Record
your measured results in Table 2
.
Circuit
Simulations
in PSPICE
Simulate the circuit in Figure 2
using PSPICE
.
Find the simulated voltage, current and
power consumption of each resistor using the voltage, current and power probes
respectively in PSPICE. Record your simulated
results in Table 2
.
D
ata
Analysis
Analyze and interpret Table 2. Include the answers to the following questions when you
are analyzing data:
What is the total current through the whole circuit? What are the currents
through R2 and R3? What is the relationship between the total
current and
the currents flowing through each resistor?
What are voltages across R2 and R3? Are they equal? If they are (not), why?
Resistors
Electrical Quantities(units)
R2
R3
Calculated Nominal
Results
Voltage
(V)
Current (mA)
Power (mW)
Measured Results
Voltage
(V)
Current (mA)
Power (mW)
Simulated Results
in PSPICE
Voltage
(V)
Current (mA)
Power (mW)
Table
2
–
DC
Parallel
Circuit Data Table
GWU SEAS ECE Department ©2010
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Exper
iment:
DC Circuits: Ohm's Law, Series and Parallel Circuits
Part
3
–
DC Series

Parallel
Combin
ation
Circuit
Circuit Measurements
Construct the circuit of Figure #
3
using your breadboard.
Use the
Agilent E3631A Triple Output DC Power Supply
as VS
3
and set the voltage
to
9
Vdc.
Use the DMM (Keithley
Model175) to measure the DC Voltage and DC Current of
R1,
R2 and R3.
Find the measured Power Consumption of
R1,
R2 and R3 from the measured DC
Voltage and DC Current of
R1,
R2 and R3.
Record your measured results in Table
3
.
Circuit
Simulations in
PSPICE
Simulate the circuit in Figure
3
using PSPICE. Find the simulated voltage, current and
power consumption of each resistor using the voltage, current and power probes
respectively in PSPICE. Record your simulated results in Table
3
.
Data Analysis
An
alyze and interpret Table 3. Include the answers to the following questions when you
are analyzing data:
What is the current through
R1
? What are the currents through R2 and R3?
What is the
mathematic
relationship
among the currents through R1, R2 and
R3?
What are voltages across
R1,
R2 and R3?
What is the mathematic
relationship among the
across
R1, R2 and R3?
Resistors
Electrical Quantities(units)
R
1
R
2
R3
Calculated
Nominal Results
Voltage
(V)
Current (mA)
Power (mW)
Measured
Results
Voltage
(V)
Current (mA)
Power (mW)
Simulated
Results in
PSPICE
Voltage
(V)
Current (mA)
Power (mW)
Table
3
–
DC
Series
–
Parallel
Combination
C
ircuit Data
Table
GWU SEAS ECE Department ©2010
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Exper
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DC Circuits: Ohm's Law, Series and Parallel Circuits
Further Analysis:
Describe
the relationship between the total currents flowing through the whole circuit and
the currents through each resistor in Figure 1, 2 and 3
,
respectively
.
Describe
the
relationship between the
source
(power supply)
voltage
and the
v
oltage
drop across
each
resistor in Figure 1, 2 and 3, respectively.
Compare the nominal results with the measured results
and the simulated results
of
Table
1,
Table
2
and Table 3
.
Explain any differences between the nominal and
measured
/simulated
results of those Data
Tables.
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