18 Electric Potential and Capacitance Lectures by James L. Pazun Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Goals for Chapter 18 To calculate electrical potential energy. To define potential. To study equipotential surfaces To review Millikans oil drop experiment. To examine capacitors. To determine electrical field energy Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Electrical potential and voltage obvious and not Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Electrical and gravitational forces - Figures The forces are similar and conservative. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Work and energy changes - Figures 18.3 Work is done on the charge by the field. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Very high energies are need to span large potentials. Lighting arcs represent billions of joules of energy. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Parallel plates and energy conservation Example 18.2 See the worked example on page 588 and Figure 18.8. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Potential of point and plate charges Examples 18.3,4 Refer to Figures 18.9 and with worked examples on pages Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley The equipotential map around charges Figure Around an charge or arrangement of charges regions of equal potential may be drawn as equal-potential lines. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Equipotential lines may not cross Figure Considering conduction and geometry one may prove why the lines do not cross. Refer to page 592 in your text. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Robert Millikan and electronic charge Figure He suspended charged oil drops of various masses between the parallel plates of a capacitor. His determination found many different multiple of *the same number*. The number was the charge of a single electron, (14)x C. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Energetics of a single electron Figure One electron suspended in a 1V field allows the definition of an energy equivalence. 1eV = 1.602x J Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley The capacitor Figures 18.17, 18 Devices may be constructed which separate two conductors of various sizes with materials of various conductance. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley The symbol and units of capacitance Figure Refer to pages 596 598 in your text. Define the Farad and follow worked examples 18.6 and 18.7. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Capacitors are often joined Figures Like resistors, capacitors may be combined sequentially (in series). Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Capacitors are often joined II Figures Like resistors, capacitors may be combined in simultaneous fashion (in parallel). Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Capacitors store energy Example 18.9 This is the whine you can hear while an electronic flash charges. Refer to the worked example on pages Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley What is between the conductors? Figures 18.26,27 As we stated on an earlier slide, the amount of charge that may be stored in a capacitor depends in part on the filler. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Capacitors with different dialectrics Figure Select the dialelectric from Table 18.1. Copyright 2012 Pearson Education, Inc. publishing as Addison-Wesley Calculation with a specific dialectric Example Refer to the worked problem on page 605 and Figure