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5-1
Electricity
Principles & Applications
Eighth Edition
Richard J. Fowler
Chapter 5
Multiple-Load Circuits
(student version)
McGraw-Hill
© 2013 The McGraw-Hill Companies Inc. All rights reserved.
5-2
INTRODUCTION
Series-Circuit Measurements (Page 107)
Series-Circuit Calculations (Page 109)
Parallel-Circuit Measurements
Parallel-Circuit Calculations
Series-Parallel Circuits
Voltage Regulation
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(Page 114)
(Page 116)
(Page 123)
(Page 128)
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5-3
Dear Student:
This presentation is arranged in segments. Each segment
is preceded by a Concept Preview slide and is followed by a
Concept Review slide. When you reach a Concept Review
slide, you can return to the beginning of that segment by
clicking on the Repeat Segment button. This will allow you
to view that segment again, if you want to.
McGraw-Hill
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5-4
Concept Preview
• Voltage drops in series are additive.
• There is only one current in a series circuit.
• Resistances in series are additive.
• Powers in a series circuit are additive.
• Ohm’s law, Kirchhoff’s voltage law, and
the power formulae are used to solve
series-circuit problems.
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5-5
Series-Circuit Relationships
mV
PT = 9 W
dc
R1
B1
90 V
RT = VT
V
COM
mA
-
A
W
(Page 00)
kW
+VAW ac
R2
R3
RT = 900 W
0.1 A
 IT = 90 V 0.1 A
= 900 W
PT = VT x IT = 90 V x 0.1 A = 9 W
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5-6
Series-Circuit Relationships
mV
V
mA
W
A
kW
PT = 9 W
PR1 = 2 W
dc
COM
-
+VAW ac
R1
VR1 = 20 V
200 W
B1
90 V
R2
R3
RT = 900 W
R1 = 200 W
0.1 A
R1 = VR1  IT = 20 V 0.1 A = 200 W
PR1 = VR1 x IT = 20 V x 0.1 A = 2 W
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5-7
Series-Circuit Relationships
mV
V
mA
W
A
kW
PT = 9 W
PR1 = 2 W
dc
COM
-
+VAW ac
PR2 = 4 W
VR1 = 20 V
R1
R2
200 W
B1
90 V
400 W
R3
RT = 900 W
R1 = 200 W
R2 = 400 W
0.1 A
VR2 = 40 V
R2 = VR2  IT = 40 V 0.1 A = 400 W
PR2 = VR2 x IT = 40 V x 0.1 A = 4 W
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5-8
Series-Circuit Relationships
mV
V
mA
W
A
kW
PT = 9 W
PR1 = 2 W
dc
COM
-
+VAW ac
PR2 = 4 W
PR3 = 3 W
VR1 = 20 V
R1
R2
R3
200 W
B1
90 V
400 W
300 W
0.1 A
RT = 900 W
R1 = 200 W
R2 = 400 W
R3 = 300 W
VR2 = 40 V
VR.3 = 30 V
R3 = VR3  IT = 30 V 0.1 A = 300 W
PR3 = VR3 x IT = 30 V x 0.1 A = 3 W
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5-9
Series-Circuit Relationships
PT = 9 W
PR1 = 2 W
Check total values against individual values
9 W = 2 W + 4W + 3 W
PR2 = 4 W
PR3 = 3 W
VR1 = 20 V
R1
R2
R3
200 W
B1
90 V
400 W
300 W
RT = 900 W
R1 = 200 W
R2 = 400 W
0.1 A
R3 = 300 W
VR2 = 40 V
VR.3 = 30 V
90 V = 20 V + 40 V + 30 V
900 W = 200 W + 400 W + 300 W
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5 - 10
Voltage Drops for Normal and Open Loads
5V
0V
12V
3V
4V
0V
Without an open load, the measured voltages are: 5V, 4V, and 3V.
With one load open, the measured voltages are: 0V, 0V, and 12V.
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5 - 11
A Series-Circuit Problem
R1
2 kW
B1
90 V
R2
VR2 =
50 V
- VR2 = 90 V - 50 V =
VR1  R1 = 40 V  2 kW =
VR1 = VT
40 V
IR1 =
20 mA
R2 = VR2 IR2 = 50 V  20 mA = 2.5 kW
RT = R1 + R2 = 2 kW + 2.5 kW = 4.5 kW
PT = IT x VT = 0.02 A x 90 V = 1.8 W
PR1 = IR1 x VR1 = 0.02 A x 40 V = 0.8 W
PR2 = IR2 x VR2 = 0.02 A x 50 V = 1.0 W
Check for errors:
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PT = PR1 + PR2 = 0.8 W + 1.0 W = 1.8 W
© 2013 The McGraw-Hill Companies Inc. All rights reserved.
5 - 12
Concept Review
• Voltage drops in series are additive.
• There is only one current in a series circuit.
• Resistances in series are additive.
• Powers in a series circuit are additive.
• Ohm’s law, Kirchhoff’s voltage law, and
the power formulae are used to solve
series-circuit problems.
Repeat Segment
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5 - 13
Concept Preview
(Page 114)
• Currents in parallel are additive.
• Only one voltage exists in a parallel circuit.
• Resistances in parallel are not additive.
• Powers in a parallel circuit are additive.
• Ohm’s law, Kirchhoff’s current law, and
the power formulae are used to solve
parallel-circuit problems.
McGraw-Hill
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5 - 14
Parallel-Circuit Relationships
mV
dc
B1
30 V
R1
V
COM
mA
-
A
W
(Page 00)
kW
+VAW ac
R2
R3
VT = VR1 = VR2 = VR3 = 30 V
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5 - 15
Parallel-Circuit Relationships
mV
dc
B1
30 V
R1
15 W
V
COM
mA
-
A
W
kW
+VAW ac
R2
R3
2A
VT = VR1 = VR2 = VR3 = 30 V
R1 = VR1 IR1 = 30 V  2 A = 15 W
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5 - 16
Parallel-Circuit Relationships
mV
dc
B1
30 V
R1
15 W
2A
V
COM
R2
30 W
mA
-
W
A
kW
+VAW ac
R3
1A
VT = VR1 = VR2 = VR3 = 30 V
R1 = VR1 IR1 = 30 V  2 A = 15 W
R2 = VR2 IR2 = 30 V  1 A = 30 W
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5 - 17
Parallel-Circuit Relationships
mV
dc
B1
30 V
R1
15 W
2A
V
COM
mA
-
W
A
+VAW ac
R2
30 W
1A
kW
R3
10 W
3A
VT = VR1 = VR2 = VR3 = 30 V
R1 = VR1 IR1 = 30 V  2 A = 15 W
R2 = VR2 IR2 = 30 V  1 A = 30 W
R3 = VR3 IR3 = 30 V  3 A = 10 W
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5 - 18
Parallel-Circuit Relationships
mV
dc
B1
30 V
V
COM
mA
-
W
A
kW
+VAW ac
R1 4 A
15 W
2A
R2
30 W
1A
R3
10 W
3A
VT = VR1 = VR2 = VR3 = 30 V
R1 = VR1  IR1 = 30 V  2 A = 15 W
R2 = VR2  IR2 = 30 V  1 A = 30 W
R3 = VR3  IR3 = 30 V  3 A = 10 W
4A = 1A + 3A
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5 - 19
Parallel-Circuit Relationships
mV
dc
V
COM
mA
-
W
A
kW
+VAW ac
R1 4 A
15 W
6A
B1
30 V
2A
R2
30 W
1A
R3
10 W
3A
VT = VR1 = VR2 = VR3 = 30 V
R1 = VR1 IR1 = 30 V  2 A = 15 W
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R2 = VR2 IR2 = 30 V  1 A = 30 W
R3 = VR3 IR3 = 30 V  3 A = 10 W
4A = 1A + 3A
IT = 2 A + 1 A + 3 A = 6 A © 2013 The McGraw-Hill Companies Inc. All rights reserved.
5 - 20
Parallel-Circuit Relationships
mV
V
mA
A
W
kW
Measured RT = 5 W
dc
COM
-
+VAW ac
R1
15 W
B1
30 V
R2
30 W
R3
10 W
Calculated total resistance is
RT =
McGraw-Hill
1 +
R1
1
1 +
R2
1
R3
=
1 +
15
1
30
=
= 5W
1 + 1
6
30
10
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5 - 21
Circuit Measurements Quiz
There is only one voltage to measure in a ____ circuit.
parallel
There is only one current to measure in a ____ circuit. series
Measuring ____ requires physical interruption of a
circuit path.
current
The easiest measurements to make in a circuit are
____ measurements.
voltage
Measuring individual resistors requires modification
of the circuit when the resistors are in ____.
parallel
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5 - 22
Concept Review
• Currents in parallel are additive.
• Only one voltage exists in a parallel circuit.
• Resistances in parallel are not additive.
• Powers in a parallel circuit are additive.
• Ohm’s law, Kirchhoff’s current law, and
the power formulae are used to solve
parallel-circuit problems.
Repeat Segment
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5 - 23
Concept Preview
• Multiple currents and voltages exist
in a series-parallel circuit.
• Two or more resistances are either in series
or parallel in a series-parallel circuit.
• Powers in a series-parallel circuit
are additive.
• Ohm’s law, Kirchhoff’s current law,
Kirchhoff’s voltage law, and power
formulae are all used to solve seriesparallel circuit problems.
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5 - 24
Solving Series-Parallel Circuits
5A
1A
B1
88 V
4A
IR4 = IR3 = 1 A
VR4 = 1 A x 33 W = 33 V
VR1 = 88 V - 48 V = 40 V
R1
8W
40 V
R2
12 W
48 V
R3
15 W
15 V
R4
33 W
33 V
RT = 88 V  5 A = 17.6 W
Cross-check
PT = 200 W + 192 W + 15 W +
33 W = 440 W
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VR3 = 48 V - 33 V = 15 V
R3 = 15 V  1 A = 15 W
IR1 = 40 V 8 W = 5 A
IR2 = 5 A - 1 A = 4 A
R2 = 48 V  4 A = 12 W
PR1 = 5 A
PR2 = 4 A
PR3 = 1 A
PR4 = 1 A
PT = 5 A
x 40 V = 200 W
x 48 V = 192 W
x 15 V = 15 W
x 33 V = 33 W
x 88 V = 440 W
© 2013 The McGraw-Hill Companies Inc. All rights reserved.
5 - 25
DETERMINING THE REGULATION OF A ZENER CIRCUIT
Determine the output voltage with the lightest load to be served.
The output voltage is 12.046 V when the load is 1000 ohms.
Notice that the 1000-ohm load draws 12 mA.
In other words, the zener provides 12.046 V when the load is 12 mA.
R1
100 W
+
0.012
A
S1
V1
25 V
12 V
D1
+
-
R2
100 W
12.046 V
R3
1000 W
Next change the load to the heaviest load to be served
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5 - 26
R1
100 W
+
0.120
V1
25 V
A
S1
12 V
D1
+
-
R2
100 W
11.916 V
R3
1000 W
Notice that S1 has been toggled to change to a 100-ohm load.
The output has reduced from 12.046 V to 11.916 V while the load current
has increased (by a factor of ten) from 12 mA to 120 mA.
The voltage source for this circuit has 5 ohms of internal resistance.
Therefore, the source voltage decreases as the load current increases.
Thus the zener is compensating for both increased load current
and decreased source voltage.
The % of V reg = [(12.046 – 11.916) / 11.916] x 100 = 1.1 %
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5 - 27
Circuit Calculations Quiz
Kirchhoff’s ____ law is most useful in solving
series circuit problems.
voltage
Kirchhoff’s ____ law is most useful in solving
parallel circuit problems.
current
Both of Kirchhoff’s laws are used in solving
____ circuit problems.
series-parallel
When a 10-W resistor and a 40-W resistor are
parallel connected to a 24-V source, the total
power is ____ watts.
72
When a 20-W resistor and a 30-W resistor are
series connected to a 25-V source, the total
power is ____ watts.
12.5
What type of diode provides good V regulation?
Zener
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5 - 28
Concept Review
• Multiple currents and voltages exist
in a series-parallel circuit.
• Two or more resistances are either in series
or parallel in a series-parallel circuit.
• Powers in a series-parallel circuit
are additive.
• Ohm’s law, Kirchhoff’s current law,
Kirchhoff’s voltage law, and power
formulae are all used to solve seriesparallel circuit problems.
Repeat Segment
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5 - 29
REVIEW
• Series-Circuit Measurements
• Series-Circuit Calculations
• Parallel-Circuit Measurements
• Parallel-Circuit Calculations
• Series-Parallel Circuits
• Voltage Regulation
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