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Lecture 5: May 29 th 2009

Lecture 5: May 29 th 2009. Physics for Scientists and Engineers II. Electric Field Calculation from Electric Potential. Example: Electric Dipole (similar to Ex. 25.4). y. P. x. q. -q. a. a. Example: Electric Dipole (similar to Ex. 25.4). y. P. x. q. -q. a. a.

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Lecture 5: May 29 th 2009

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  1. Lecture 5: May 29th 2009 Physics for Scientists and Engineers II Physics for Scientists and Engineers II , Summer Semester 2009

  2. Electric Field Calculation from Electric Potential Physics for Scientists and Engineers II , Summer Semester 2009

  3. Example: Electric Dipole (similar to Ex. 25.4) y P x q -q a a Physics for Scientists and Engineers II , Summer Semester 2009

  4. Example: Electric Dipole (similar to Ex. 25.4) y P x q -q a a Physics for Scientists and Engineers II , Summer Semester 2009

  5. Example: Electric Dipole (similar to Ex. 25.4) y P q -q x x-a x+a Physics for Scientists and Engineers II , Summer Semester 2009

  6. Example: Electric Dipole (similar to Ex. 25.4) Physics for Scientists and Engineers II , Summer Semester 2009

  7. Example: Electric Dipole (similar to Ex. 25.4) y Physics for Scientists and Engineers II , Summer Semester 2009

  8. Electric Potential Due to Continuous Charge Distributions dq r P Physics for Scientists and Engineers II , Summer Semester 2009

  9. Example y a P(x=a,y=b) dq=ldx r b x O x dx L Physics for Scientists and Engineers II , Summer Semester 2009

  10. Example Physics for Scientists and Engineers II , Summer Semester 2009

  11. Example Physics for Scientists and Engineers II , Summer Semester 2009

  12. Example: Chapter 25, Problem 38 R 2R 2R O Find the electric potential at O. Linear charge density = l. Three contributions to V: left straight piece, curved piece, and right straight piece. Physics for Scientists and Engineers II , Summer Semester 2009

  13. Example: …and another one -Q R R R +Q O Find the electric potential at O. Charge +Q is evenly distributed. Physics for Scientists and Engineers II , Summer Semester 2009

  14. Electric Potential Due to a Charged Conductor Charged conductor in electrostatic equilibrium (no net charge movement) B C A The electric potential is constant throughout a charged conductor in electrostatic equilibrium. Physics for Scientists and Engineers II , Summer Semester 2009

  15. Electric Potential and Field of a Charged Spherical Conductor + + + + + + + + + + + + V E Physics for Scientists and Engineers II , Summer Semester 2009

  16. Two Connected Charged Spheres (far apart, so electric field of one sphere does not significantly the affect charge distribution on the other sphere) r1 q1 metal wire r2 q2 Physics for Scientists and Engineers II , Summer Semester 2009

  17. Two Connected Charged Spheres (far apart) Physics for Scientists and Engineers II , Summer Semester 2009

  18. Electric Field in the Cavity within a Conductor Charged conductor in electrostatic equilibrium (no net charge movement) B A Physics for Scientists and Engineers II , Summer Semester 2009

  19. Chapter 26: Capacitance and Dielectrics Assume you have two charged conductors having equal but opposite amounts of charge on them: +Q -Q Physics for Scientists and Engineers II , Summer Semester 2009

  20. Definition of “Capacitance” Physics for Scientists and Engineers II , Summer Semester 2009

  21. The Plate Capacitor -Q • A battery has a potential difference DV (“voltage”) • between it’s two terminals. • Assume: Before the wires are connected, Q=0 on the plates. • 1) There will be an electric field within the wire going from the left plate to the negative terminal and 2) There will be an electric field within the wire going from the positive terminal to the right plate. Electrons will move opposite to the field lines (from the negative terminal to the left plate and from the right plate to the positive terminal) • The left plate gets charged negatively and the right plate gets charged positively as electrons leave it. +Q Area = A d - + • The increasing charges on the plates create an increasing additional • electric field in the wires, opposite to that produced by the battery • terminals. • Once enough charge is on the plates, the electric field in the wires is zero. • The capacitor is now “fully charged”. • The higher the voltage of the battery, the more charge can accumulate on the capacitor. Physics for Scientists and Engineers II , Summer Semester 2009

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