Download video slide - Web.NMSU.Edu Web Publishing Services

Chapter 26
Direct-Current Circuits
PowerPoint® Lectures for
University Physics, Twelfth Edition
– Hugh D. Young and Roger A. Freedman
Lectures by James Pazun
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Goals for Chapter 26
• To study resistors in series and parallel
• To consider Kirchoff’s Rules
• To see the design and learn about the use of
electronic measuring instruments
• To mentally assemble R-C circuits
• To study the applications of circuits in household
wiring
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Introduction
• In the last chapter, we gained
insight about how current flows
through a resistor in simple
examples like a light bulb
attached to a battery.
• Now, imagine many thousands
of circuits wired onto flat
wafers with structure so tiny
that microscopy would be
necessary to view their patterns.
Understanding the next step and
mastering more complex circuit
patterns is the goal for
Chapter 26.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Resistors in series and parallel I
• If we took three resistors
and considered the different
ways they could be
connected, we arrive at the
four possibilities illustrated
in Figure 26.1.
• Some of the combinations
will be sequential (like the
line at a phone booth), some
will be en masse (like a
marching band moving in
rows). The former are
analogous to resistors in
series, the latter to resistors
in parallel.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Resistors in series and parallel II
• If you have ever wired a Christmas tree with a series of lights
(resistors) in series, you know what happens if just one burns out.
The lights have become an open circuit and will not function.
• Car headlights are a good example of resistors wired in parallel. If
one light burns out, the circuit changes but still functions to allow
the driver a safe trip to repair. See Figure 26.2 below.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Resistors in series and parallel III—combinations
• Consider Problem-Solving Strategy 26.1.
• Follow Example 26.1 guided by Figure 26.3 below.
• Follow Example 26.2.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Kirchoff’s Rules I—junctions
• The algebraic sum of the currents into any junction is zero.
Figures 26.6 and 26.7 illustrate this rule and are shown below.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Kirchoff’s Rules II—loops
• The algebraic sum of the potential differences in any loop,
including those associated with emfs and those of resistive
elements, must equal zero.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Kirchoff’s Rules III—examples and strategy
• Read through Problem-Solving Strategy 26.2. Figure 26.9
illustrates this strategy.
• Refer to Example 26.3, illustrated by Figure 26.10.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Kirchoff’s Rules IV—examples
• Refer to Example 26.4, illustrated by Figure 26.11.
• Consider Example 26.5.
• Refer to Example 26.6, illustrated by Figure 26.12.
• Review Example 26.7.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
D’Arsonval’s galvanometer
• We’ll call it simply “meter” henceforth.
• The meter is a coil of wire mounted next to a permanent
magnet. Any current passing through the coil will induce
magnetism in the coil. The interaction of the new
electromagnetism and the permanent magnet will move the
meter indicator mounted to the coil.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
The ammeter
• The ammeter (sometimes prefixed with milli or micro because the
currents to be measured are routinely thousandths or millionths of
an ampere) may be used to measure current OR voltage. A shunt
resistor makes this conversion as shown below in Figure 26.15.
• Consider Example 26.8 to follow a current example. Consider
Example 26.9 to follow a voltage example.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Ammeters and voltmeters in combination
• An ammeter and a voltmeter may be used together to measure
voltage and power.
• Figure 26.16 below illustrates meters set to measure resistance.
• Refer to Example 26.10.
• Follow Example 26.11.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Ohmmeters and digital multimeters
• An ohmmeter is designed specifically to measure resistance.
• Refer to Figure 26.17 and Figure 26.18 below to see an
ohmmeter wiring diagram and a photograph of a digital
multimeter. The multimeter can measure current, voltage, or
resistance over a wide range.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
R-C circuits
•
Some excellent examples of variable resistance and potential are likely common
to our experience.
•
The physiology of a heartbeat, the medical intervention of a pacemaker, and
charging a capacitor to take a flash picture are ideas shown below in Figures
26.20 and 26.21.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Charging, discharging and timing …
• Consider Figures 26.23 and 26.24.
• Follow Examples 26.12 and 26.13.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Power distribution systems—a home
• Potential, resistors, outlets, input from the power company … no
wonder electricians are integral contractors in home construction!
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
Fuses, circuit breakers, and GFI
•
A fuse will melt and a breaker will
open the circuit if maximum current
is reached. See Figure 26.26.
•
GFI stops further current flow when a
sudden drop in resistance indicates
that someone has offered a new path
to ground. I don’t know if it will save
this worker we see in Figure 26.27
who didn’t use a grounded drill.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley
The wiring diagram for a typical kitchen
• Consider Figure 26.28 below.
• Follow Example 26.14.
Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley