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Physics 014

Physics 014. Electric Potential 2. Topics. Point charge potential Point charge (group) potential Continuous charge potential Fields from potential Conductors. Potentials and Fields. We take the line integral (a particular path) between two points i and f. Here choose V i as

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Physics 014

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  1. Physics 014 Electric Potential 2

  2. Topics • Point charge potential • Point charge (group) potential • Continuous charge potential • Fields from potential • Conductors

  3. Potentials and Fields • We take the line integral (a particular path) between two points i and f. Here choose Vi as the reference point

  4. Potentials and Fields

  5. ??? • For a family of equipotential surfaces and five paths of an electron, (a) what is the direction of the E field for the surfaces, (b) for each path, is the work +,-, or 0, (c) rank the paths according to work we do, greatest first.

  6. Potential of a point charge • Using the integral expression for potential,

  7. Potential of a point charge

  8. Potential of a point charge • A positively charged particle produces a positive electric potential. A negatively charged particle produces a negative potential.

  9. Potential of a group • For n charges, we sum the potentials,

  10. ??? The figure shows three arrangements of two protons. Rank the arrangements according to the net electric potential produced at point P by the protons, greatest first.

  11. Continuous charge potential • For continuous charge distributions, use differential elements of charge, Differential charge Differential potential

  12. Continuous charge potential: Line

  13. Continuous charge potential: Disk

  14. Fields from Potential • The component of E in any direction is the negative of the rate at which the electric potential changes with distance in that direction. “Partial derivative of V with respect to y”

  15. Fields from Potential • For a uniform electric field, • Δs is the distance traveled perpendicular to potential surfaces

  16. ??? • Three pairs of plates have the same separation. The fields are uniform. (a) Rank the pairs according to field. Greatest first. (b) Which pair is the field to the right? (c) An electron midway between the plates in (3) stands still, has constant velocity, or accelerates?

  17. Energy of a system • The electric potential energy of a system of fixed point charges is equal to the work that must be done by an external agent to assemble the system, bringing each charge in from an infinite distance.

  18. Energy of a system • For the pair of point charges from the diagram, Work done by me to move q2 into position from infinity

  19. Potential for conductors • An excess charge placed on an isolated conductor will distribute itself on the surface of that conductor so that all points on the conductor come to the same potential. Even if a cavity exists within the conductor.

  20. Quiz Friday • 24-1, 24-2, 24-3, 24-5, 24-6

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