Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley PowerPoint ® Lectures for University Physics, Twelfth Edition – Hugh D. Young and Roger A. Freedman Lectures by James Pazun Chapter 26 Direct-Current Circuits

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 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 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 Figure 26.9 illustrates this strategy. Refer to Example 26.3, illustrated by Figure

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Kirchoff’s Rules IV—examples Refer to Example 26.4, illustrated by Figure Consider Example Refer to Example 26.6, illustrated by Figure 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 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 below illustrates meters set to measure resistance. Refer to Example Follow Example

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 and Figure 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 and

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Charging, discharging and timing … Consider Figures and Follow Examples and

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 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 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 below. Follow Example