Chapter 19

1. Chapter 19 Current, Resistance, and Directed-Current Circuits

2. Goals for Chapter 19 • To understand the concept of current. • To study resistance and Ohm’s Law. • To observe examples of electromotive force and circuits to learn Ohm’s Law’s application. • To calculate the energy and power in electric circuits. • To study the similarity and differences in the combination of resistors in parallel and those connected in series. • To apply Kirchhoff’s Rules to combinations of resistors. • To observe and understand devices which measure electricity in circuits. • To combine resistors and capacitors then calculate examples of the results.

3. Current defined – Figures 19.1 and 19.2

4. How many electrons are moving – Example 19.1 • See Figure 19.3 and the worked example on page 620.

5. Resistance as defined by Ohm’s Law - Figure 19.4 • The resistance of an object in a circuit may be calculated from the voltage and current in a closed circuit. • Refer to the top of page 621. • Commercial resistors carry coded labels.

6. Using the color code Band Color As # As a multiplier Black 0 1 Brown 1 10 Red 2 100 Orange 3 1,000 Yellow 4 10,000 Green 5 100,000 Blue 6 1,000,000 Violet 7 10,000,000 Gray 8 100,000,000 White 9 1,000,000,000 Tolerance Code None 20% Silver 10% Gold 5% • You can determine the resistance in ohms. • Try the one on the previous page. • 5700 ohms • +/- 570 ohms

7. Resistivity – Figure 19.5 and Example 19.2 • Refer to worked example on pages 623-624 in your text. The problems make use of Table 19.1

8. Electromotive force – Figures 19.10, 19.11 The potential difference can draw an analogy from a waterfall.

9. Electricity flowing – Example 19.4 This worked example is also well supported by Conceptual Analysis 19.2. Supporting Analysis 19.2 Supporting Example 19.4

10. Each circuit may be drawn symbolically. Each device will be represented by brief symbols. The utility of the method becomes clear as soon as soon as you must represent a car or a blender. There are too many parts to draw them as they actually appear.

11. Several examples of circuits with different elements Refer to worked examples 19.5, 19.6, 19.7. The same basic elements are arranged on slightly different parallel or series combinations. Notice the dramatic differences. Refers to example 19.6 Refers to example 19.7

12. Consider time and potential changes – Pages 629-630 Potential change, current flow, and time allow us to speak in terms of power. In general terms Refer to page 629. In the human body Refer to page 630.

13. Pure resistance and energy conservation - Figure 19.18 The text on pages 630-631 draw details leading to Quantitative Analysis 19.4.

14. Connections in series and/or parallel - Figure 19.19 Like capacitors in the previous chapter, resistors can be connected end-to-end (series) or simultaneously (parallel).

15. Combinations of series and parallel arrangements The Problem Solving Strategy 19.1, Examples 19.9 and Figures 19.20 and19.22.

16. Kirchhoff’s Rules – Figure 19.23 Many actual networks cannot be described with simple series-parallel combinations. What then? One method is described by Gustav Kirchhoff in the 1800s.

17. Water pipe analogy and application – Figures 19.24-25 Once we understand the analogy, we can apply it to the Quantitative Analysis 19.5.

18. Recharging situations – Figures 19.28 and 19.29 Rechargeable batteries and jump-starting a dead car battery contain some complexities. Refer to Examples 19.10 and 19.11.

19. Devices to make measurement – Figures 19.30, 19.31 Voltmeters, ammeters, resistance gauges, digital multimeters are all at our disposal. Some are more traditional like the generic galvanometer at left; some are newer and digital, like the multimeter on the right.

20. Resistors and capacitors combine – Figures 19.32, 33 Combinations of resistors and capacitors form what are called RC Devices. A camera flash storing charge is a good example.