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Chapter 19

Chapter 19. Electric Potential Energy and the Electric Potential. Objectives. Electric potential energy Electric potential difference Conservation of energy Equipotential surfaces and their relation to the electric field Capacitors and dielectrics

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Chapter 19

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  1. Chapter 19 Electric Potential Energy and the Electric Potential

  2. Objectives • Electric potential energy • Electric potential difference • Conservation of energy • Equipotential surfaces and their • relation to the electric field • Capacitors and dielectrics • Biomedical applications of electric • potential differences

  3. Potential Energy

  4. The Electric Potential Difference The electric potential V at a given point is the electric potential energy EPE of a small test charge qo situated at that point divided by the charge itself. SI Unit: joule/coulomb = volt (V)

  5. The Electric Potential Difference One electron volt is the amount by which the potential energy of an electron changes when it moves through a potential difference of one volt: 1eV = 1.60X10-19 J

  6. Potential Energy

  7. Potential Energy

  8. The Electric Potential Difference Created by Point Charges Potential of a point charge

  9. Potential Energy Example Determine the number of particles, each carrying a charge of 1.60 X 10-19 C that pass between the terminals of a 12-V car battery when a 60.0-W headlight burns for one hour. (p. 561)

  10. The Electric Potential Difference Created by Point Charges

  11. The Electric Potential Difference Created by Point Charges Example At locations A and B, find the total electric potential due to the two point charges. (p. 565) V = +240 V At any location, the total electric potential is the algebraic sum of the individual potentials created by each point charge that is present!

  12. Potential Energy Known variables: e = 1.60 X 10-19 C ∆V = 12-V Power = 60.0 W Unknown variables: Energy= q0= N= Formulae:

  13. Potential Energy of a Group of Charges Example The figure shows three point charges; initially they are infinitely far apart. They are then brought together and placed at the corners of an equilateral triangle. Each side as a length of 5.0 m. Determine the electric potential energy of the triangular group. (p. 567)

  14. Potential Energy of a Group of Charges Example EPEtot=EPE1 + EPE2 +EPE3 EPEtot= +0.14 J

  15. Conservation of Energy Total = Translational + Rotational + Gravitational Energy Kinetic energy Kinetic Energy Potential Energy + Spring + Electric Potential Energy Potential Energy

  16. Conservation of Energy a) A particle has a mass of m = 1.8 X 10-5 kg and a positive charge of q0 = +3.0 X 10-5 C. It is released from point A and accelerates horizontally until it reaches point B. The only force acting on the particle is an electric force and the electrical potential at a is 25 V greater tan at B. What is the speed vB of the particle when it reaches point B? (p. 562)

  17. Conservation of Energy Known variables: m=1.8 X 10-5 kg q0 = 3.0 X 10-5 C VA-VB = 25-V Unknown variables: vB = Formulae:

  18. Conservation of Energy b) A particle has a mass of m = 1.8 X 10-5 kg and a negative charge of q0 = -3.0 X 10-5 C. It is released from point B and accelerates horizontally until it reaches point A. The only force acting on the particle is an electric force and the electrical potential at A is 25 V greater tan at B. What is the speed vA of the particle when it reaches point A? (p. 562)

  19. Conservation of Energy Known variables: m=1.8 X 10-5 kg q0 = 3.0 X 10-5 C VA-VB = 25-V Unknown variables: vA = Formulae:

  20. Equipotential Surfaces

  21. Equipotential Surfaces

  22. Electrical Potential Surfaces

  23. Equipotential Surfaces and their Relation to the Electric Field

  24. Capacitors and Dielectrics Random-Access Memory Chips

  25. Capacitors The Relation between Charge and Potential Difference for a Capacitor The magnitude q of the charge on each plate of a capacitor is directly proportional to the magnitude V of the potential difference between the plates: where C is the capacitance. SI Unit: coulomb/volt= farad (F)

  26. Dielectrics and the Dielectric Constant Dielectric Constant

  27. Dielectrics and the Dielectric Constant

  28. Dielectrics and the Dielectric Constant Example The capacitance of an empty capacitor is 1.2F. The capacitor is connected to a 12-V battery and charged up. With the capacitor connected to the battery, a slab of dielectric material is inserted between the plates. As a result, 2.6 X 10-5 C of additional charged flows from one plate, through the battery, and onto the other plate. What is the dielectric constant  of the material? (p. 572) Known Variables C0 = 1.2F V= 12 –V q-q0= 2.6 X 10-5 C Unknown Variables  = Formulae 1) 2)

  29. Energy Storage in a Capacitor

  30. Biomedical Applications of Electric Potential Differences Electroencephalography Electroretinography Electrocardiography

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