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-Electric Potential Energy -Electric Potential

-Electric Potential Energy -Electric Potential. AP Physics C Mrs. Coyle. Gravitational Potential Energy. A. Higher Potential Energy. D U A->B = U B -U A = - W field. Lower Potential Energy. B. Consider a positive test charge in the following electric field. +. A.

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-Electric Potential Energy -Electric Potential

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  1. -Electric Potential Energy -Electric Potential AP Physics C Mrs. Coyle

  2. Gravitational Potential Energy A Higher Potential Energy DUA->B= UB-UA= - Wfield Lower Potential Energy B

  3. Consider a positive test charge in the following electric field. + A Higher Potential Energy DUA->B= UB-UA= - Wfield Lower Potential Energy B

  4. Electric Potential Energy When a point charge qo is in an electric field E: • The force from the field is F=qoE • The work that the force of the electric field does to move the charge from point A to B (in the direction of the field) is W=Fd • As the charge is moved by the electric force it loses potential energy but gains kinetic energy.

  5. Change in Electric Potential Energy • Change in Electric Potential Energy • (Final PE- Initial PE) DUA->B= UB-UA= - Wfield • The (-)sign (- Wfield )indicates the loss of potential energy when the charge moves in the direction of the field.

  6. The Electric Force is Conservative • The force, F = qoE, caused by the electric field and experience by the charge is conservative. That is: • The work done by the conservative force does not depend on the path taken. • A trip back to the original position would have a change in energy of zero.

  7. ds Consider an infinitesimal displacement vector , ds, that is oriented tangent to a path through space.

  8. The work done by the electric field is W = F.ds = qoE.ds • As this work is done by the field, the potential energy of the charge-field system is changed by ΔU = -qoE.ds • For a finite displacement of the charge from A to B,

  9. Change in potential energy of the system.

  10. Electric Potential Energy • Which point is at a higher electric potential energy location? Consider a positive test charge.

  11. If qo is negative, then ΔU is positive when the charge is moved in the direction of the electric field by an external force. • Consider the analogy of a bow and arrow. If you pull back the arrow from the bow, the arrow will gain potential energy. • In order for a negative charge to move in the direction of the field, an external agent must do positive work on the charge.

  12. Electric Potential Difference (Voltage ): work per unit charge required to move a charge between two positions in an electric field. • DV =W/q , qo is a positive test charge • Scalar • Unit: 1 Volt = 1 J / C • It takes one joule of work to move a 1-coulomb charge through a potential difference of 1 volt

  13. Electric Potential • The potential energy per unit charge, U/qo, is the electric potential • The potential is independent of the value of qo • The potential has a value at every point in an electric field • The electric potential is

  14. Electric Potential • The potential is a scalar quantity • As a charged particle moves in an electric field, it will experience a change in potential

  15. Using Conservation of Energy • Using conservation of energy, if the voltage difference is known, the potential energy difference can be calculated for a given charge. • If all the potential energy is converted to kinetic energy, then final speed can be calculated.

  16. Electron-Volts • A unit of energy • One electron-volt is defined as the energy a charge-field system gains or loses when a charge of magnitude e (an electron or a proton) is moved through a potential difference of 1 volt • 1 eV = 1.60 x 10-19 J • Remember that e=1.60 x 10-19 C

  17. Summary of Charged Particle Released from Rest in a Uniform Field • A positive charge released from rest moves in the direction of the electric field. • The change in potential is negative. • The change in potential energy is negative. • The force and acceleration are in the direction of the field.

  18. Potential in a Uniform Electric Field • ΔV=-Ed • E=-ΔV/dThe negative sign indicates that the electric potential at point B is lower than at point A • Another unit for electric field is: 1 V/m= 1 N/C • We can interpret the electric field as the change of the electric potential with position.

  19. Electric Potential • Which point is at a higher electric potential?

  20. Note: • Electric Field lines point to the lower potential

  21. Note: • Electric potential is independent of any test charges that may be placed in the field. • Electric potential is a characteristic of the field.

  22. Equipotentials • Point B is at a lower potential than point A • Points B and C are at the same potential • Equipotential surface is a surface consisting of a continuous distribution of points having the same electric potential

  23. Equipotentials and Field Lines • Equipotential surfaces are always perpendicular to field lines.

  24. Equipotential Lines Simulation of Field with Equipotential Lines http://glencoe.mcgraw-hill.com/sites/0078458137/student_view0/chapter21/electric_fields_applet.html

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