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 23 Electric Potential

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Goals for Chapter 23 To study and calculate electrical potential energy To define and study examples of electric potential To trace regions of equal potential as equipotential surfaces To find the electric field from electrical potential

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Introduction Electrical potential is sometimes modeled as a river. The width of the river defines how much water will be able to flow through its banks. The arc welder in the picture at right is taking advantage of a potential between the welding rod and material to be joined. The arc of electrical flow is so hot that the metals and the rod actually melt into one material.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Work, energy, and the path from start to finish The work done raising a basketball against gravity depends only on the potential energy, how high the ball goes. It does not depend on other motions. A point charge moving in a field exhibits similar behavior. Refer to Figures 23.1 and 23.2 below.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley An electric charge moving in an electric field

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley A test charge will move with respect to other charges A test charge will move directly away from a like charge q.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The work done moving a test charge As a test charge moves away from a charge of like sign, the path does not matter (with respect to work or energy), only the distance between the charges.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Potential energy curves—PE versus r Graphically, the potential energy between like charges increases sharply to positive (repulsive) values as the charges become close. Unlike charges have potential energy becoming sharply negative as they become close (attractive). Refer to Example 23.1.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Electrical potential and multiple point charges The potential between multiple charges is done by vector addition of the individual energies as shown in Figure Figure 23.9 shows this principle is applied to an ion engine for spaceflight. Refer to Example 23.2.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The electrical potential The potential of a battery can be measured between point a and point b (the positive and negative terminals). Moving with the electrical field decreases the electrical potential. Moving against the field lowers it.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley A particle accelerator imparts amazingly large energies A particle accelerator can bring a charged particle to motion at velocities great enough to impart millions, even billions, of eV as kinetic energy. Figure at right shows a particle accelerator at the Fermi Lab in Illinois. Refer to Example 23.3.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Finding the potential Refer to Example 23.4—multiple charges. This example is illustrated by Figure Refer to Example 23.5—potential and potential energy. Refer to Example 23.6—potential by integration. This example is illustrated by Figure Refer to Example 23.7—potential by integration. This example is illustrated by Figure

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Calculation of electrical potential Consider Problem-Solving Strategy Refer to Example 23.8 with Figure

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Example—oppositely charged parallel plates Refer to Example 23.9 using Figure

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Example—a charged, conducting cylinder Refer to Example using Figure

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Example—a ring of charge Refer to Example using Figure

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Example—a line of charge Refer to Example using Figure

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Equipotential surfaces and field lines Surfaces of equal potential may be drawn any charge or charges and the field lines they create.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Field lines and a conducting surface Refer to Figure to illustrate the concept of field lines near a conducting surface.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The surface and interior of a conductor

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Potential and fields of charge Follow Example to calculate the potential and field of a point charge. Follow Example to calculate the potential and field of a ring of charge.