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OBJECTIVES
After studying Chapter 5, the reader should be able to:
1. Prepare for ASE Electrical/Electronic Systems
(A6) certification test content area “A” (General
Electrical/Electronic System Diagnosis).
2. Identify a series circuit.
3. State Kirchhoff’s voltage law.
4. Calculate voltage drops in a series circuit.
5. Explain series circuit laws.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SERIES CIRCUITS
• A series circuit is a complete circuit that has more
than one electrical load where all of the current has
only one path to flow through all of the loads.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OHM’S LAW AND SERIES CIRCUITS
• Ohm’s law can be used to
calculate the value of one
unknown (voltage,
resistance, or amperes) if
the other two values are
known.
FIGURE 5-1 A series circuit with three bulbs. All current
flows through all resistances (bulbs). The total resistance
of the circuit is the sum of the total resistance of the bulbs,
and the bulbs will light dimly because of the increased
resistance and the reduction of current flow (amperes)
through the circuit.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OHM’S LAW AND SERIES CIRCUITS
FIGURE 5-2 A series circuit with two bulbs.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
KIRCHHOFF’S VOLTAGE LAW
• Kirchhoff’s voltage law, concerns voltage drops. It
states:
– The voltage around any closed circuit is equal to the sum
(total) of the voltage drops across the resistances.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
KIRCHHOFF’S VOLTAGE LAW
Applying Kirchhoff’s Voltage Law
FIGURE 5-3 As current flows through a circuit, the voltage drops in proportion
to the amount of resistance in the circuit. Most, if not all, of the resistance
should occur across the load such as the bulb in this circuit. All of the other
components and wiring should produce little, if any, voltage drop. If a wire or
connection did cause a voltage drop, less voltage would be available to light
the bulb and the bulb would be dimmer than normal.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
KIRCHHOFF’S VOLTAGE LAW
Applying Kirchhoff’s Voltage Law
FIGURE 5-4 In a series circuit, the voltage is dropped or lowered by each
resistance in the circuit. The higher the resistance, the greater the drop in voltage.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
KIRCHHOFF’S VOLTAGE LAW
Applying Kirchhoff’s Voltage Law
FIGURE 5-5 A voltmeter reads the differences of voltage between the test leads. The voltage read
across a resistance is the voltage drop that occurs when current flows through a resistance. A voltage
drop is also called an “IR” drop because it is calculated by multiplying the current (l) through the
resistance (electrical load) by the value of the resistance (R).
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
KIRCHHOFF’S VOLTAGE LAW
Use of Voltage Drops
• Voltage drops, due to built-in resistance, are used in
automotive electrical systems to drop the voltage in
the following examples.
– Dash lights
– Blower motor
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
KIRCHHOFF’S VOLTAGE LAW
Voltage Drops as a Testing Method
• Any resistance in a circuit causes the voltage to
drop in proportion to the amount of the resistance.
• The formula for voltage drop is:
– E = I x R where E is the voltage drop and I is the current
in the circuit.
– Notice that as the value of the resistance (R ) increases,
the voltage drop increases.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SERIES CIRCUIT LAWS
• Electrical loads or resistance connected in series
behave following series circuit laws.
– Law 1 The total resistance in a series circuit is the sum
total of the individual resistances.
– Law 2 The current is constant throughout the entire
circuit.
– Law 3 Although the current (in amperes) is constant, the
voltage drops across each resistance in the circuit.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SERIES CIRCUIT LAWS
FIGURE 5-6 In this series circuit with a 2 ohm resistor and a 4 ohm
resistor, the current (2 amperes) is the same throughout, even though the
voltage drops across each resistor.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SERIES CIRCUIT EXAMPLES
FIGURE 5-7 Example 1.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SERIES CIRCUIT EXAMPLES
FIGURE 5-8 Example 2.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SERIES CIRCUIT EXAMPLES
FIGURE 5-9 Example 3.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SERIES CIRCUIT EXAMPLES
FIGURE 5-10 Example 4.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
SUMMARY
1. In a simple series circuit, the current remains
constant throughout, but the voltage drops as
current flows through the resistances of the circuit.
2. The voltage drop across each resistance or load is
directly proportional to the value of the resistance
compared to the total resistance in the circuit.
3. The sum (total) of the voltage drops equals the
applied voltage (Kirchhoff’s voltage law).
4. An open or a break anywhere in a series circuit
stops all current from flowing.
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
REVIEW QUESTIONS
1. What is Kirchhoff’s voltage law?
2. What would current (amperes) do if the
voltage were doubled in a circuit?
3. What would current (amperes) do if the
resistance in the circuit were doubled?
4. What is the formula for voltage drop?
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
1. The amperage in a series circuit is _____.
a) The same anywhere in the circuit
b) Variable in the circuit due to the different resistances
c) High at the beginning of the circuit and decreases as
the current flows through the resistance
d) Always less returning to the battery than leaving the
battery
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
1. The amperage in a series circuit is _____.
a) The same anywhere in the circuit
b) Variable in the circuit due to the different resistances
c) High at the beginning of the circuit and decreases as
the current flows through the resistance
d) Always less returning to the battery than leaving the
battery
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
2. The sum of the voltage drops in a series circuit
equals the _____.
a)
b)
c)
d)
Amperage
Resistance
Source voltage
Wattage
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
2. The sum of the voltage drops in a series circuit
equals the _____.
a)
b)
c)
d)
Amperage
Resistance
Source voltage
Wattage
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
3. If the resistance and the voltage are known, what
is the formula for finding the current (amperes)?
a)
b)
c)
d)
E=IxR
I=ExR
R=ExI
I = E/R
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
3. If the resistance and the voltage are known, what
is the formula for finding the current (amperes)?
a)
b)
c)
d)
E=IxR
I=ExR
R=ExI
I = E/R
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
4. A series circuit has three resistors of 6 ohms each.
The voltage drop across each resistor is 4 volts.
Technician A says that the source voltage is 12
volts. Technician B says that the total resistance is
18 ohms. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
4. A series circuit has three resistors of 6 ohms each.
The voltage drop across each resistor is 4 volts.
Technician A says that the source voltage is 12
volts. Technician B says that the total resistance is
18 ohms. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
5. If a 12 volt battery is connected to a series circuit
with three resistors of 2 ohms, 4 ohms, and 6
ohms, how much current will flow through the
circuit?
a)
b)
c)
d)
1 ampere
2 amperes
3 amperes
4 amperes
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
5. If a 12 volt battery is connected to a series circuit
with three resistors of 2 ohms, 4 ohms, and 6
ohms, how much current will flow through the
circuit?
a)
b)
c)
d)
1 ampere
2 amperes
3 amperes
4 amperes
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
6.
A series circuit has two 10 ohm bulbs. A third 10 ohm bulb
is added in series. Technician A says that the three bulbs
will be dimmer than when only two bulbs were in the
circuit. Technician B says that the current in the circuit will
increase. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
6.
A series circuit has two 10 ohm bulbs. A third 10 ohm bulb
is added in series. Technician A says that the three bulbs
will be dimmer than when only two bulbs were in the
circuit. Technician B says that the current in the circuit will
increase. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
7. Technician A says that the sum of the voltage
drops in a series circuit should equal the source
voltage. Technician B says that the current
(amperes) varies depending on the value of the
resistance in a series circuit. Which technician is
correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
7. Technician A says that the sum of the voltage
drops in a series circuit should equal the source
voltage. Technician B says that the current
(amperes) varies depending on the value of the
resistance in a series circuit. Which technician is
correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
8.
Two light bulbs are wired in series and one bulb burns out
(opens). Technician A says that the other bulb will work.
Technician B says that the current will increase in the
circuit because one electrical load (resistance) is no longer
operating. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
8.
Two light bulbs are wired in series and one bulb burns out
(opens). Technician A says that the other bulb will work.
Technician B says that the current will increase in the
circuit because one electrical load (resistance) is no longer
operating. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
9.
Four resistors are connected to a 12 volt battery in series.
The values of the resistors are 10 ohms, 100 ohms, 330
ohms, and 470 ohms. Technician A says that the greatest
voltage drop will occur across the 10 ohm resistor.
Technician B says that the greatest voltage drop will occur
across the 470 ohm resistor. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
9.
Four resistors are connected to a 12 volt battery in series.
The values of the resistors are 10 ohms, 100 ohms, 330
ohms, and 470 ohms. Technician A says that the greatest
voltage drop will occur across the 10 ohm resistor.
Technician B says that the greatest voltage drop will occur
across the 470 ohm resistor. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
10. Three light bulbs are wired in series. A fourth bulb
is connected to the circuit in series. Technician A
says that the total voltage drop will increase.
Technician B says that the current (amperes) will
decrease. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
CHAPTER QUIZ
10. Three light bulbs are wired in series. A fourth bulb
is connected to the circuit in series. Technician A
says that the total voltage drop will increase.
Technician B says that the current (amperes) will
decrease. Which technician is correct?
a)
b)
c)
d)
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
END
Diagnosis and Troubleshooting of Automotive Electrical,
Electronic, and Computer Systems, Fifth Edition
By James D. Halderman
© 2010 Pearson Higher Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458