1. 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 24 Capacitance and Dielectrics

2. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Goals for Chapter 24 To consider capacitors and capacitance To study the use of capacitors in series and capacitors in parallel To determine the energy in a capacitor To examine dielectrics and see how different dielectrics lead to differences in capacitance

3. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Introduction When flash devices made the “big switch” from bulbs and flashcubes to early designs of electronic flash devices, you could use a camera and actually hear a high-pitched whine as the “flash charged up” for your next photo opportunity. The person in the picture on page 815 must have done something worthy of a picture. Just think of all those electrons moving on camera flash capacitors!

4. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Keep charges apart and you get capacitance Any two charges insulated from each other form a capacitance. Refer to Figure 24.1 below.

5. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley How do we build a capacitor? What’s it good for?

6. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The unit of capacitance, the farad, is very large Commercial capacitors for home electronics are often cylindrical, from the size of a grain of rice to that of a large cigar. Capacitors like those mentioned above and pictured at right are microfarad capacitors.

7. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Some examples of flat, cylindrical, and spherical capacitors See just how large a 1 F capacitor would be. Refer to Example 24.1. Refer to Example 24.2 to calculate properties of a parallel-plate capacitor. Follow Example 24.3 and Figure 24.5 to consider a spherical capacitor. Follow Example 24.3 and Figure 24.5 to consider a cylindrical capacitor.

8. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Capacitors may be connected one or many at a time Connection “one at a time” in linear fashion is termed “capacitors in series.” This is illustrated in Figure 24.8. Multiple connections designed to operate simultaneously is termed “capacitors in parallel.” This is illustrated in Figure 24.9.

9. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Calculations regarding capacitance Refer to Problem-Solving Strategy 24.1. Follow Example 24.5. Follow Example 24.6. The problem is illustrated by Figure 24.10 below.

10. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The Z Machine—capacitors storing large amounts of energy This large array of capacitors in parallel can store huge amounts of energy. When directed at a target, the discharge of such a device can generate temperatures on the order of 10 9 K!

11. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Dielectrics change the potential difference The potential between to parallel plates of a capacitor changes when the material between the plates changes. It does not matter if the plates are rolled into a tube as they are in Figure 24.13 or if they are flat as shown in Figure 24.14.

12. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Table 24.1—Dielectric constants

13. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Field lines as dielectrics change Moving from part (a) to part (b) of Figure 24.15 shows the change induced by the dielectric.

14. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Examples to consider, capacitors with and without dielectrics Refer to Problem-Solving Strategy 24.2. Follow Example 24.10 to compare values with and without a dielectric. Follow Example 24.11 to compare energy storage with and without a dielectric. Figure 24.16 illustrates the example.

15. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Dielectric breakdown A very strong electrical field can exceed the strength of the dielectric to contain it. Table 24.2 at the bottom of the page lists some limits.

16. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Molecular models Figure 24.18 (at right) and Figure 24.19 (below) show the effect of an applied field on individual molecules.

17. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Polarization and electric field lines

18. Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Gauss’s Law in dielectrics Refer to Figures 24.22 and 24.23 to illustrate Gauss’s Law in dielectrics. Follow Example 24.12.