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Chapter 20 Electric Potential Energy and Potential

Physics 314. Chapter 20 Electric Potential Energy and Potential. Agenda 2/9/2015. Review Electrostatics Test Commonly missed questions Retake policy Potential Energy Demonstration Notes on Electric Potential Energy Practice problems for EPE. Retake Policy.

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Chapter 20 Electric Potential Energy and Potential

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  1. Physics 314 Chapter 20Electric Potential Energy and Potential

  2. Agenda 2/9/2015 • Review Electrostatics Test • Commonly missed questions • Retake policy • Potential Energy Demonstration • Notes on Electric Potential Energy • Practice problems for EPE

  3. Retake Policy • Must complete any missing work from the unit first!! • Must complete assigned problem set and review answers with Mr. Gustin. • Meetings must take place before the next test date.

  4. Energy • Energy is the ability to do work. • Measured in joules • 1J = 1 N*m • Forms of Energy: • Kinetic Energy: Energy of Motion • Potential Energy: Energy of Position • Nuclear Energy: Energy of the Atom

  5. Work • This is a measure of the change in energy in a system. • Represented by variable W. • Work = Force * distance • Both quantities must be present for work to be done • Demo: Physical Science Textbook

  6. Gravitational Potential Energy • The energy of position is called potential energy • The higher you raise the book off the ground the greater the GPE of the object. • The more WORK the object CAN do.

  7. Electric Potential Energy • A charged object can have a potential based on its position in an electric field or its position based on another charged particle. • Think about holding two positive charges very close together.

  8. GPE: Ug=mgh EPE: Ue = kq1q2/d • Directly related to height • Larger height => Larger Energy • Based on gravitational pull • Greater G => Greater Energy • Inversely related to distance • Smaller dist. => Larger Energy • Based on strength of E-Field • Greater E => Greater Energy A Brief Comparison

  9. Agenda 2/10/2015 • Review Potential Energy • EPE and GPE • Practice Problems • Introduce Potential • Gravitational Potential • Electric Potential (Voltage) • HW: EPE Problem Set

  10. Energy • Ability to accomplish work • Measured in joules (J) • Variable shown as U in text • Forms: kinetic-energy of motion (KE, UK) potential-energy of position (PE, UG, UE) nuclear-energy of the atom

  11. Work • Equal to the change in energy of a system W = ΔU • Work has to be done to a charge to increase its potential energy • Work is done by a charge to decrease its potential energy

  12. Increasing Electric Potential Energy • Just as an object raised to a higher height has more of an ability to exert a greater force onto the ground at landing, a negative charge moved in the direction of a field has more UE (EPE)

  13. Electric Potential (Voltage) • Ratio of potential energy to charge V = Electric potential energy test charge’s charge V = UE/qo • For potential created by a point charge… V = kq/r **like with E fields, potential exists and is the same at a given location no matter which charge is there and even if NO charge is there to feel it SCALAR QUANTITY

  14. Electric Potential vs. UE • Potential same but UE different (dependent upon test charge) at same spot in space

  15. Electric potential difference • Same as voltage in circuits • If potential difference exists, work will be done. • Charges will be moved (current) ΔV = Vb – Va = +W/qo = +ΔPE/qo W = +q ΔV • If no potential difference exists between points no work is done…no current • Equipotential

  16. Example Problem • How much work is needed to change the potential of an electron exactly 5.00V?

  17. Example Problem • What is the electric potential difference for a positive charge of value 2.0 x 10-6 C if it is moved closer to another positive charge, requiring 4.0 x 10-4 J of work?

  18. Agenda 2/11/2015 • Review EPE Homework • Exit Slip • Review Electric Potential • Equipotential • Gravitational Potential Analogy PhET • Sheet Demo • Where is work done?? • HW: Electric Potential Problem Set

  19. Electric Potential • What is the potential at a point that is located 3.3mm left of a 20C source? • What about to the right? • Above? • Below?

  20. Potential is like Elevation • Think of a topographical map. • Each line represents the same elevation. • Masses will roll downhill, toward smaller numbers

  21. Equipotential • Places of equal potential in a diagram with electric charges

  22. Equipotentials vs. Electric Field Lines • No arrows on equipotentials • List Potential somewhere on equipotential • Have equal increments between shown equipotentials • All equipotentials strike electric field lines at right angles

  23. Agenda 2/12/2015 • Potential Difference Warm Up • Review Electric Potential PS • Can you feel the Potential Difference? • Equipotential Between plates • EP Lines between plates • HW: Potential Difference Practice

  24. Potential Difference Problem • What is the electric potential difference for a positive charge of value 2.0 x 10-6 C if it is moved closer to another positive charge, requiring 4.0 x 10-4 J of work for this to happen?

  25. Electric Potential Difference in a Constant Electric field Between two plates the E-Field lines run from + to – plates. How should the EP lines be drawn?

  26. Electric potential difference • Critical Thinking: • In order for work to be done on a charge, what must happen? • How would an electron move between these two plates? • What is it called when electrons flow/move? e-

  27. Agenda 2/13/2015 • Parallel Plate Warm-Up • Potential Difference and Potential Energy • Potential Difference Demo • w/ Van DeGraff Generator • Potential Pennies Lab • What are the differences between V and J • Practice Work and Potential Energy • HW: TBD

  28. Example: ΔV vs. ΔEPE _- - - - - - - - - - - - - - - - - - - - - 1. Find the change in potential (ΔV) of a 2.0 C Charge moved from point P to Point Q they are 3cm apart. 2. What is ΔV for this charge going from P to R 3cm apart? 3. P to S 3cm apart? • P to T 3cm apart? E = 5.0 V/m Q Q T P R T P R S S ++++++++++++++++++++++

  29. Agenda 2/17/2015 • Potential Energy Warm-Up • What’s the difference? • Potential Energy • Electric Potential • E-Fields • Begin Unit Review • TEST ON WEDNESDAY • HW: Complete Unit Review

  30. Example: ΔV vs. ΔEPE _- - - - - - - - - - - - - - - - - - - - - 1. Find the change in potential energy (ΔEPE) of a 2.0 C charge moved from point P (0,0) to Point Q (0,3). 2. What is ΔEPE for this charge going from P to R (3,0)? 3. P to S (0,-3)? 4. P to T (-3,0)? E = 5.0 V/m Q T P R S ++++++++++++++++++++++

  31. Agenda 2/18/2015 • Test Moved to Thursday • Review Questions from the Study Guide • Specific Topics • Review Equation Sheets • Specific Variables and Units • New Review Sheet • HW: Complete New Unit Review

  32. What is the magnitude of an electric field existing between two electrodes of a parallel-plate capacitor with a separation distance of 7.50 mm and potential difference of 300 V?

  33. How much work energy is required to raise the electric potential of an electron exactly 5.00 V? • 8 x 10-19J

  34. What is the electric potential exactly 2.00 cm away from a bare proton? What is the electric potential exactly 3.00 cm away from a bare proton? What is the potential difference between the two locations? • A) 7.2 x 10^-8V • B) 4.8 x 10^-8V • C) 2.4 x 10 ^-8 V

  35. What is the total electric potential upon a point Z located 5.00 cm from a charge of 6.00 C if another charge with magnitude 3.00 C is located on a line 8.00 cm beyond the first one? • 6C= 1.08 x 10^12 V • 3C = 3.4 x 10^11 V • Total = 1.42 x 10^12 V

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