Download Chapter 32

Chapter 32. Fundamentals of Circuits
Chapter 32. Fundamentals of Circuits
Surprising as it may seem,
the power of a computer is
achieved simply by the
controlled flow of charges
through tiny wires and
circuit elements.
Chapter Goal: To
understand the fundamental
physical principles that
govern electric circuits.
Topics:
• Circuit Elements and Diagrams
• Kirchhoff’s Laws and the Basic Circuit
• Energy and Power
• Series Resistors
• Real Batteries
• Parallel Resistors
• Resistor Circuits
• Getting Grounded
• RC Circuits
1
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
2
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
How many laws are named after Kirchhoff?
A.
B.
C.
D.
E.
Chapter 32. Reading Quizzes
0
1
2
3
4
3
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
4
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
How many laws are named after Kirchhoff?
A.
B.
C.
D.
E.
0
1
2
3
4
What property of a real battery makes
its potential difference slightly different
than that of an ideal battery?
A.
B.
C.
D.
E.
Short circuit
Chemical potential
Internal resistance
Effective capacitance
Inductive constant
5
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
In an RC circuit, what is the
name of the quantity
represented by the symbol τ?
What property of a real battery makes
its potential difference slightly different
than that of an ideal battery?
A.
B.
C.
D.
E.
6
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
A.
B.
C.
D.
E.
Short circuit
Chemical potential
Internal resistance
Effective capacitance
Inductive constant
Period
Torque
Terminal voltage
Time constant
Coefficient of thermal expansion
7
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
8
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
In an RC circuit, what is the
name of the quantity
represented by the symbol τ?
A.
B.
C.
D.
E.
Which of the following are ohmic materials:
A. batteries.
B. wires.
C. resistors.
D. Materials a and b.
E. Materials b and c.
Period
Torque
Terminal voltage
Time constant
Coefficient of thermal expansion
10
9
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Which of the following are ohmic materials:
A. batteries.
B. wires.
C. resistors.
D. Materials a and b.
E. Materials b and c.
The equivalent resistance for a group of
parallel resistors is
A.
B.
C.
D.
E.
less than any resistor in the group.
equal to the smallest resistance in the group.
equal to the average resistance of the group.
equal to the largest resistance in the group.
larger than any resistor in the group.
11
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
12
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
The equivalent resistance for a group of
parallel resistors is
A.
B.
C.
D.
E.
less than any resistor in the group.
equal to the smallest resistance in the group.
equal to the average resistance of the group.
equal to the largest resistance in the group.
larger than any resistor in the group.
Chapter 32. Basic Content and Examples
13
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
14
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
15
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
16
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Tactics: Using Kirchhoff’s loop law
17
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
18
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Tactics: Using Kirchhoff’s loop law
19
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
20
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Energy and Power
EXAMPLE 32.4 The power of light
The power supplied by a battery is
QUESTION:
The units of power are J/s, or W.
The power dissipated by a resistor is
Or, in terms of the potential drop across the resistor
21
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
22
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
EXAMPLE 32.4 The power of light
EXAMPLE 32.4 The power of light
23
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
24
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Series Resistors
EXAMPLE 32.4 The power of light
• Resistors that are aligned end to end, with no
junctions between them, are called series resistors or,
sometimes, resistors “in series.”
• The current I is the same through all resistors placed
in series.
• If we have N resistors in series, their
equivalent resistance is
The behavior of the circuit will be unchanged if the N series
resistors are replaced by the single resistor Req.
25
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
26
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
EXAMPLE 32.7 Lighting up a flashlight
QUESTION:
27
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
28
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
EXAMPLE 32.7 Lighting up a flashlight
EXAMPLE 32.7 Lighting up a flashlight
29
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
30
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
EXAMPLE 32.7 Lighting up a flashlight
EXAMPLE 32.7 Lighting up a flashlight
31
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
32
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Parallel Resistors
EXAMPLE 32.10 A combination of resistors
• Resistors connected at both ends are called
parallel resistors or, sometimes, resistors “in parallel.”
• The left ends of all the resistors connected in parallel
are held at the same potential V1, and the right ends are
all held at the same potential V2.
• The potential differences ∆V are the same across
all resistors placed in parallel.
• If we have N resistors in parallel, their
equivalent resistance is
The behavior of the circuit will be unchanged if the N
parallel resistors are replaced by the single resistor Req.
QUESTION:
33
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
34
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
EXAMPLE 32.10 A combination of resistors
EXAMPLE 32.10 A combination of resistors
35
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
36
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Example: Kirchoff’s Rules
EXAMPLE 32.10 A combination of resistors
+
I
∆V2
−
R3
I3
R2
I2
R1
+
I
−
∆V
∆
V1
I = I 2 + I3
−I3R3 + I2R2 = 0
∆V1 − ∆V2 − I2R2 − IR1 = 0
37
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
38
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
RC Circuits
• Consider a charged capacitor, an open switch, and
a resistor all hooked in series. This is an RC Circuit.
• The capacitor has charge Q0 and potential difference
∆VC = Q0/C.
• There is no current, so the potential difference across
the resistor is zero.
• At t = 0 the switch closes and the capacitor begins
to discharge through the resistor.
• The capacitor charge as a function of time is
where the time constant τ is
39
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
40
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
EXAMPLE 32.14 Exponential decay in an RC
circuit
EXAMPLE 32.14 Exponential decay in an RC
circuit
QUESTION:
41
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
42
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
EXAMPLE 32.14 Exponential decay in an RC
circuit
EXAMPLE 32.14 Exponential decay in an RC
circuit
43
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
44
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
General Strategy
Chapter 32. Summary Slides
45
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
46
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
General Strategy
General Strategy
47
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
48
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Important Concepts
Important Concepts
49
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
50
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Important Concepts
Applications
51
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
52
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Applications
Chapter 32. Questions
53
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
54
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Which of these diagrams represent the same circuit?
A. a and b
B. b and c
C. a and c
D. a, b, and d
E. a, b, and c
Which of these diagrams represent the same circuit?
A. a and b
B. b and c
C. a and c
D. a, b, and d
E. a, b, and c
55
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
56
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
What is ∆V across the
unspecified circuit
element? Does the
potential increase or
decrease when
traveling through this
element in the direction
assigned to I?
What is ∆V across the
unspecified circuit
element? Does the
potential increase or
decrease when
traveling through this
element in the direction
assigned to I?
A. ∆V decreases by 2 V in the direction of I.
B. ∆V increases by 2 V in the direction of I.
C. ∆V decreases by 10 V in the direction of I.
D. ∆V increases by 10 V in the direction of I.
E. ∆V increases by 26 V in the direction of I.
A. ∆V decreases by 2 V in the direction of I.
B. ∆V increases by 2 V in the direction of I.
C. ∆V decreases by 10 V in the direction of I.
D. ∆V increases by 10 V in the direction of I.
E. ∆V increases by 26 V in the direction of I.
57
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Rank in order, from largest to smallest,
the powers Pa to Pd dissipated in
resistors a to d.
A.
B.
C.
D.
E.
58
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Rank in order, from largest to smallest,
the powers Pa to Pd dissipated in
resistors a to d.
Pb > Pa = Pc = Pd
Pb = Pd > Pa > Pc
Pb = Pc > Pa > Pc
Pb > Pd > Pa > Pc
Pb > Pc > Pa > Pd
A.
B.
C.
D.
E.
Pb > Pa = Pc = Pd
Pb = Pd > Pa > Pc
Pb = Pc > Pa > Pc
Pb > Pd > Pa > Pc
Pb > Pc > Pa > Pd
60
59
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
What is the potential at points a to e ?
What is the potential at points a to e ?
A.
A.
B.
B.
C.
D.
E.
C.
D.
E.
61
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
62
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
Rank in order,
from brightest to
dimmest, the
identical bulbs A
to D.
Rank in order,
from brightest to
dimmest, the
identical bulbs A
to D.
A. C = D > B > A
B. A > C = D > B
C. A = B = C = D
D. A > B > C = D
E. A > C > B > D
A. C = D > B > A
B. A > C = D > B
C. A = B = C = D
D. A > B > C = D
E. A > C > B > D
63
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
64
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
The time constant
for the discharge of
this capacitor is
The time constant
for the discharge of
this capacitor is
A. 5 s.
B. 1 s.
C. 2 s.
D. 4 s.
E. The capacitor doesn’t discharge because
the resistors cancel each other.
A. 5 s.
B. 1 s.
C. 2 s.
D. 4 s.
E. The capacitor doesn’t discharge because
the resistors cancel each other.
65
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.
66
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley.