Physics 2402
Department of Physics and Geology
Series and parallel circuits
Purpose:
To understand the two basic ways of combining resistors to circuits.
Materials:
Frederiksen Power Supply 0-24V AC/DC 3630.00
Extech Instruments AC/DC Clamp Meter 380950
Pasco EM-8656 AC/DC Electronics Laboratory
One Red connecting wires
One Blue/Black connecting wire
One packaged of assorted wires
Assorted resistors 10Ω, 22Ω, 68Ω, 91Ω, 100Ω, 130Ω, 150Ω , and 1000Ω
Part 1: Series Circuits
Theory:
Four resistors are said to be connected in series when they are wired as shown below:
In a series circuit the same current flows through each resistor but the voltage across each resistor is different. Each
resistor produces a voltage drop, the size of which is given by Ohm's law
V=IR
The sum of all the voltage drops in a circuit is equal to the voltage drop across an equivalent circuit in which all the
resistors are replaced by an equivalent resistance.
VTotal =IReq
where Req =R1+R2+R3
In this lab we will experimentally measure the voltage drop across one or more resistors using a multi-meter. This
value will then be compared with the value obtained from Ohm's Law.
Experimental Procedure:
1) Plug the Frederiksen Power Supply 0-24V AC/DC 3630.00 the wall socket using universal power cable.
DO NOT TURN ON DEVICES
2) Connect a red wire to the (+DC) port on the Frederiksen Power Supply 0-24V AC/DC 3630.00 to the
Pasco EM-8656 AC/DC Electronics Laboratory terminal.
3) Connect a blue/black wire to the (-DC) port on the Frederiksen Power Supply 0-24V AC/DC 3630.00 to
the Pasco EM-8656 AC/DC Electronics Laboratory terminal.
4) Select 4 (four) resistors from the bin
5) Sort the 4(resistors) in order with least resistance first and greatest resistance last from the color code table
and record into table 1.
6) Plug red probe into red socket labeled (V Hz) on Extech Instruments AC/DC Clamp Meter 380950
7) Plug black probe into black socket labeled (COM) on Extech Instruments AC/DC Clamp Meter 380950
8) Turn knob on Extech Instruments AC/DC Clamp Meter 380950 to the function.
9) Use Extech Instruments AC/DC Clamp Meter 380950 to confirm the color code resistance by placing the
black and red probe on the ends of each resistor.
10) Record results into Table 1
11) Turn on Frederiksen Power Supply 0-24V AC/DC 3630.00
12) On the DC side of the Frederiksen Power Supply 0-24V AC/DC 3630.00; set voltage to 3V
13) Turn off Frederiksen Power Supply 0-24V AC/DC 3630.00 when voltage is set
14) Turn knob on Extech Instruments AC/DC Clamp Meter 380950 to the
function
15) Use Extech Instruments AC/DC Clamp Meter 380950 by placing the red probe in a coil that is attached to
the red wire from the Frederiksen Power Supply 0-24V AC/DC 3630.00, place the black probe in a coil that
is attached to the blue/black wire from the Frederiksen Power Supply 0-24V AC/DC 3630.00.
16) Record the result of the voltage and use this value for theoretical voltage
17) Place Least resistance resistor in series onto Pasco EM-8656 AC/DC Electronics Laboratory.
18) Turn the knob on the Extech Instruments AC/DC Clamp Meter 380950 to the 4A with a dashed line under a
solid line
19) Clamp the blue/black line
20) Press the ZERO button on the Extech Instruments AC/DC Clamp Meter 380950
21) Turn on Frederiksen Power Supply 0-24V AC/DC 3630.00 that is set to 3V.
22) Record the reading from the Extech Instruments AC/DC Clamp Meter 380950 in the EXPERIEMENTAL
CURRENT.
23) Use the probes on the Extech Instruments AC/DC Clamp Meter 380950 that is set to the
function.
Touch the probe ends to each end of the resistor.
24) Record the amperage from the Frederiksen Power Supply 0-24V AC/DC 3630.00 in Table 2. Use this
for your theoretical amperage.
Revised January 2012
25)
26)
27)
28)
29)
30)
Record the voltage across the resistor into Table 2.
Use the measured resistance as the actual resistance.
R theoretical is the color coded value
Calculate the theoretical voltage and theoretical amperage.
Calculate the % error of both experimental and theoretical.
Repeat steps 17-29 adding a new resistor to the existing resistor until all 4 resistors are placed in
series.
Table 1. Resistor values
Resistance ( )Extech Instruments
Color Code
Resistance ( ) color code
R1
R2
R3
R4
Table 2. One resistor case
Experimental
I=______A
Experimental Voltage (V)
V1=
V1=
Resistor ( )
R1 color code=
R1 measured=
AC/DC Clamp Meter 380950
Theoretical I=_______A
Theoretical Voltage (V=IR)
VT=
VT=
=________
RTheoretical = R1 =________
%errorexp =
=_____ %error theoretical =
Table 3. Two resistor case
Experimental
I=_______A
Experimental Voltage (V)
V1=
V2=
V1=
V2=
Resistor ( )
R1color code=
R2color code=
R1measured=
R2measrued=
Vtotal = V1+V2=______V
=_________
RTheoretical = R1+R2 =________
Revised January 2012
=_____
Theoretical
I=_________A
Theoretical Voltage (V=IR)
VT=
VT=
VT=
VT=
%errorexp =
=_______
Table 4. Three resistor case
Experimental
%error theoretical =
I=____________A
Experimental Voltage (V)
V1=
V2=
V3=
V1=
V2=
V3=
Resistor ( )
R1color code=
R2color code=
R3color code=
R1measrued=
R2measured=
R3measured=
=_________
Theoretical
I=____________A
Theoretical Voltage (V=IR)
VT=
VT=
VT=
VT=
VT=
VT=
Vtotal = V1+V2+V3=______V
=_______
RTheoretical = R1+R2+R3 =_______
%errorexp =
=________
Table 5. Four resistor case
Experimental
%error theoretical =
I=________A
Experimental Voltage Drop (V)
V1=
V2=
V3=
V4=
V1=
V2=
V3=
V4=
Resistor ( )
R1color code=
R2 color code =
R3 color code =
R4 color code =
R1measured=
R2 measured =
R3measured =
R4 measured =
=________
Theoretical
I=__________A
Theoretical Voltage Drop (V=IR)
VT=
VT=
VT=
VT=
VT=
VT=
VT=
VT=
V total = V1+V2+V3+V4=________V
=______
R Theoretical = R1+ R2+R3+R4 =______
%error exp =
Revised January 2012
=________
%error theoretical =
=_________
Part 2: Parallel Circuits
Theory:
In a parallel circuit, the voltage across each branch of the circuit is the same as the total voltage across the circuit.
For this simple circuit, the amount of current in each branch is given by Ohm's law:
V=IR
Therefore
The sum of the currents through all the branches in this circuit is equal to the total current through an equivalent
circuit in which all the resistors are replaced by an equivalent resistance,
Vtotal =ItotalRtotal
where
Itotal= I1+I2+I3+I4
from above
and
and Vtotal = V because, as stated above, the voltage across each branch is the same as the total. In this lab we will
measure the total current and voltage in a parallel circuit and use them to compute the equivalent resistance of the
circuit. We will then compare this to the theoretical value of the equivalent resistance.
Revised January 2012
Experimental Procedure:
1) Following the same procedures as in PART 1
2) Start with the two least resistant resistors and place them in parallel on the Pasco EM-8656 AC/DC
Electronics Laboratory as shown above.
3) Follow steps 18-29 in Part 1, use measured results of resistors.
Table 6. Two Resistor Case
Resistor (Ω)
R1=
R2=
Experiment
Voltage (V)
V1=
V2=
*compute theoretical values from
for each resistor.
Vtotal= ______________ V from direct measurement
Itotal =_______________A from direct measurement
Itotal =________________A by adding currents I1 and I2
=________________
=______________
% error in Rtotal= _______________
Revised January 2012
from direct measurements
calculated
Theory*
Current (A)
I1 =
I2 =
Table 7. Three Resistor Case
Experiment
Voltage (V)
V1=
V2=
V3=
Resistor ()
R1=
R2=
R3=
*compute theoretical values from
Theory*
Current (A)
I1 =
I2 =
I3 =
for each resistor.
Vtotal= _______________ V from direct measurement
Itotal =________________A from direct measurement
Itotal =________________A by adding currents I1, I2 and I3
=________________
from direct measurements
=______________
calculated
% error in Rtotal= _______________
Table 8. Four Resistor Case
Experiment
Voltage (V)
V1=
V2=
V3=
V4=
Resistor ()
R1=
R2=
R3=
R4=
*compute theoretical values from
for each resistor.
Vtotal= _______________ V from direct measurement
Itotal =________________A from direct measurement
Itotal =________________A by adding currents I1, I2, I3 and I4
=________________
from direct measurements
=______________
% error in Rtotal= _________
Revised January 2012
calculated
Theory*
Current (A)
I1 =
I2 =
I3 =
I4 =
Questions:
1) If voltage is energy. What happens to the energy when there is a voltage differential across a resistor?
2) How do you account for the difference between the %error experimental and %error theoretical? Why is
this important?
3) What is the purpose of the color code system of resistors?
Labeling Resistors
Printed on each resistor are four colored bands which contain the information on the resistance. The first band (the
one closest to the end) gives the first digit, the second band tells the second digit and the third band gives the factor
often these numbers must be multiplied by. The fourth band provides information about the accuracy of the resistor
and will not be used in this lab. In the example below a resistor has the band red, yellow, red and brown. By using
the table below we see that the value of this resistor is 2400 .
R
2
Y
R
4
10
B
2
0
24x102 = 2400Ω
Color
Revised January 2012
Number
Multiplier
Black
0
1
Brown
1
101
Red
2
102
Orange
3
103
Yellow
4
104
Green
5
105
Blue
6
106
Violet
7
107
Grey
8
108
White
9
109
Gold
10-1
Silver
10-2