chapter 26 reading quiz ac circuits - physics & astronomytitle: microsoft powerpoint -...
TRANSCRIPT
• AC sources
• Resistor circuits and AC power
• The transmission and use of electricity
• Capacitor circuits
Chapter 26
AC Circuits
Topics:
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
• Capacitor circuits
• Inductors and inductor circuits
• Oscillation circuits
Sample question:Transmission lines carry alternating current at voltages as high as 500,000 V. Why are such high voltages used? And why can birds
perch safely on such high-voltage wires?
Transmission lines carry alternating current at voltages as high as 500,000 V. Why are such high voltages used? And why can birds
voltage wires?
Slide 26-1
Reading Quiz
1. What is the name of the device that is used to change the voltage of AC electricity?
A. Reactor
B. Circuit breaker
C. Inductor
D. Transformer
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What is the name of the device that is used to change the
Slide 26-2
1. What is the name of the device that is used to change the
voltage of AC electricity?
D. Transformer
Answer
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
What is the name of the device that is used to change the
Slide 26-3
Reading Quiz
2. What quantity with units of ohms, besides resistance, is
introduced in this chapter?
A. Inductance
B. Reactance
C. GFI
D. Transformance
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What quantity with units of ohms, besides resistance, is
Slide 26-4
2. What quantity with units of ohms, besides resistance, is introduced in this chapter?
B. Reactance
Answer
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What quantity with units of ohms, besides resistance, is
Slide 26-5
An AC Voltage Source
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The circuit symbol for an AC voltage source
Slide 26-6
Resistor Circuits
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Resistor Voltages and Currents
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vR = VR co
iR =vR
R=
VR cos 2
R
Lowercase symbols represent
instantaneous values of current or
voltage. They change sinusoidally with
time.
Resistor Voltages and Currents
Uppercase symbols represent
peak values of current or
voltage. They are fixed
quantities.
os 2π f t
2π f t= IR cos 2π f t
Slide 26-8
AC Power in Resistors
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PR =1
2IR
2R
Average power loss in a
resistor with peak current IR
2
Slide 26-9
If we define
Root-Mean-Square Current and Voltage
Irms =IR
2and
then we can write
PR =IR
2
R = (
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PR =2
R = (
and
PR = I rms( )2
R =Vrm(
R
The expressions for AC power are identical to those used for DC
currents if rms currents and voltages are used.
Square Current and Voltage
Vrms =VR
2
Irms( )2
RIrms( ) R
ms )2
R= IrmsVrms
The expressions for AC power are identical to those used for DC
currents if rms currents and voltages are used.
Slide 26-10
Transformers
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Transformer voltages for primary and
secondary coils with
V2 =N2
N1
V1 or
Transformer voltages for primary and
secondary coils with N1 and N2 turns
(V2 )rms =N2
N1
(V1)rms
Slide 26-11
Checking Understanding
Suppose that an ideal transformer has 10 turns in its primary coil
and 20 turns in its secondary coil. The current through the primary coil is shown in the graph on the upper left. Which of the other graphs best represents the current through the secondary coil?
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Suppose that an ideal transformer has 10 turns in its primary coil
and 20 turns in its secondary coil. The current through the primary coil is shown in the graph on the upper left. Which of the other graphs best represents the current through the secondary coil?
Slide 26-12
Answer
Suppose that an ideal transformer has 10 turns in its primary coil and 20 turns in its secondary coil. The current through the primary coil is shown in the graph on the upper left. Which of the other graphs best represents the current through the secondary coil?
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Suppose that an ideal transformer has 10 turns in its primary coil and 20 turns in its secondary coil. The current through the primary coil is shown in the graph on the upper left. Which of the other graphs best represents the current through the secondary coil?
Slide 26-13
Transmission of Electrical Power
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Transmission of Electrical Power
Slide 26-14
Two-Phase Power
to Your Home
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Wiring Inside the Home
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Physiological Effects and Electrical Safety
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Physiological Effects and Electrical Safety
Slide 26-17
Electrical Dangers
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Capacitor Circuits
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vC = VC cos 2π f t
Slide 26-19
Voltage, Charge, and
Current for a Capacitor in
an AC Circuit
IC = (2π f C)VC =VC
XCXC
XC =1
2π f C
where
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Capacitive Reactance
X =1
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XC =1
2π f C
Slide 26-21
Inductance and Inductors
vL = L∆iL
∆t
1 henry = 1
Units of inductance:
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The circuit symbol for an inductor
1 henry = 1
1 H = 1 V ⋅ s/A = 1 Ω ⋅ s
Slide 26-22
Inductor Circuits
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Inductor Currents and Voltages
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Inductor Currents and Voltages
Slide 26-24
Inductive Reactance
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VL = (2π f L)IL
IL =VL
2π f L=
VL
XL
or
2π f L XL
XL = 2π f L
where
Slide 26-25
LC Circuits
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Energy of an LC Circuit and a Block on a Spring
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Circuit and a Block on a Spring
f =1
2π
k
m
Block on spring:
f =1
2π
1
LC
LC circuit:
Slide 26-27
The RLC Circuit
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The Driven RLC Circuit
f0 =1
2π
1
LC
Imax =
Ε0
R
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The Driven RLC Circuit for Different Values of
I =Ε0
R2
+ XL − XC( )2
=
R
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Circuit for Different Values of R
Ε0
R2
+ 2π f L − 1 / 2π f C( )2
Slide 26-30