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Chapter 30

Chapter 30. Current and Conductivity. When there is current, the bulb glows and the compass needle deflects. Current. Electron Current ( i ). i = electrons/sec n = electrons/m 3. v d  10 -4 m/s. Question.

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Chapter 30

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  1. Chapter 30 Current and Conductivity Phys 133 – Chapter 30

  2. When there is current, the bulb glows and the compass needle deflects. Current Phys 133 – Chapter 30

  3. Electron Current (i) i = electrons/sec n = electrons/m3 vd 10-4 m/s Phys 133 – Chapter 30

  4. Question The light switch is located approximately 2 m from the light. How long will it take an electron to travel this distance? (vD=10-4 m/s) Do Workbook 28.7 Phys 133 – Chapter 30

  5. Electrons cannot be created or destroyed (conservation of charge) Conservation of electron current The electron current is the same at all points in a current-carrying wire. The electron current into a junction is the same as the electron current leaving a junction. Phys 133 – Chapter 30

  6. need an electric field How to create current static dynamic (not static equilibrium) Phys 133 – Chapter 30

  7. Surface charges make E field - creates current What creates Electric Field? Phys 133 – Chapter 30

  8. Do Workbook 28.8 & 9 Phys 133 – Chapter 30

  9. Battery: charge escalator “Pump”, no charge created Move charge against electric field Battery Phys 133 – Chapter 30

  10. Current (I)(as opposed to electron current) Current - amount of charge passing per unit time Current Density -charge passing per unit time per unit area Phys 133 – Chapter 30

  11. (conservation of charge/current) Kirchoff’s junction rule Phys 133 – Chapter 30

  12. Phys 133 – Chapter 30

  13. Collisions/energy transfer No electric field With electric field Electrons move randomly Electrons tend to move against electric field Phys 133 – Chapter 30

  14. Conduction/resitivity -Fields cause current (add energy) -Collisions (take away energy) -Current density (J) linear in electric field -Depends on conductivity (resistivity) -material dependent -environment (temperature, magnetic field, …) Phys 133 – Chapter 30

  15. Simulation Phys 133 – Chapter 30

  16. Problem 28.33 The electron beam inside a TV tube is 0.4 mm in diameter with current 50 A. Electrons strike screen. How many electrons strike screen each second? What is the current density in the beam? The electrons move at 4.0x107m/s. What electric field is necessary to accelerate the electrons to this speed over a distance of 5.0 mm? Assume each electron gives its kinetic energy to the screen. What power is delivered to the screen? Phys 133 – Chapter 30

  17. Problem 28.33 ans How many electrons strike screen each second? What is the current density in the beam? The electrons move at 4.0x107m/s. What electric field is necessary to accelerate the electrons to this speed over a distance of 5.0 mm? Assume each electron gives its kinetic energy to the screen. What power is delivered to the screen? Phys 133 – Chapter 30

  18. Potential in a circuit/wire Apply to wire Phys 133 – Chapter 30

  19. Potential and current in a wire Phys 133 – Chapter 30

  20. “Ohmic” vs “non-ohmic” materials Phys 133 – Chapter 30

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