Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Electric potential energy Electric potential Conservation of energy Chapter 21 Electric Potential Topics: Sample question: Shown is the electric potential measured on the surface of a patient. This potential is caused by electrical signals originating in the beating heart. Why does the potential have this pattern, and what do these measurements tell us about the heart’s condition? Slide 21-1

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Chapter 21 Key Equations (2) Key Energy Equations from Physics 152 Electric Potential Energy for 2 point charges (zero potential energy when charges an infinite distance apart)  Potential Energy for a uniform infinite plate For one plate, zero potential energy is at infinity For two plates, zero potential energy is at one plate or inbetween the two plates Electric Potential V and Change in Electric Potential =>  V Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Example: Electric Potential Energy A cart on a track has a large, positive charge and is located between two sheets of charge. Initially at rest at point A, the cart moves from A to C. a.Draw qualitative force diagrams for the cart at positions A, B and C. b.Draw qualitative energy bar charts for the cart when it is at each position A, B and C. List the objects that make up your system: c. How would your force and energy diagrams change (if at all) if the sheet to the right were also positively charged? Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Changes in Electric Potential Energy  PE e For each situation below, identify which arrangement (final or initial) has more electrical potential energy within the system of charges and their field. Slide Initial Final Greatest  PE e (a) (b) (c) (d)Hydrogen Atom

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Changes in Electric Potential Energy  PE e For each situation below, identify which arrangement (final or initial) has more electrical potential energy within the system of charges and their field. Slide Initial Final Greatest  PE e (e) (f) (g)

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Changes in Electric Potential Energy  PE e Is the change ∆PE e of a charged particle positive, negative, or zero as it moves from i to f? (a) Positive (b) Negative (c) Zero (d) Can’t tell Slide 21-11

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Chapter 21 Key Equations (3) Key Points about Electric Potential Electric Potential increases as you approach positive source charges and decreases as you approach negative source charges (source charges are the charges generating the electric field) A line where  V= 0 V is an equipotential line (The electric force does zero work on a test charge that moves on an equipotential line and  PE e = 0 J) For a point charge For very large charged plates, must use Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Electric Potential and E-Field for Three Important Cases Slide 21-25

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Checking Understanding Rank in order, from largest to smallest, the electric potentials at the numbered points. Slide 21-14

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Example A proton has a speed of 3.5 x 10 5 m/s at a point where the electrical potential is 600 V. It moves through a point where the electric potential is 1000 V. What is its speed at this second point? Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Example A proton has a speed of 3.5 x 10 5 m/s at a point where the electrical potential is 600 V. It moves through a point where the electric potential is 1000 V. What is its speed at this second point? Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

A Topographic Map Slide 21-12

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Graphical Representations of Electric Potential Slide 21-13

Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Example A proton has a speed of 3.5 x 10 5 m/s at a point where the electrical potential is 600 V. It moves through a point where the electric potential is 1000 V. What is its speed at this second point? Slide Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.

Electric Potential Energy Slide 21-9

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Electric Potential Slide 21-10