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Exploring Electric Potential and Signal Generation in Physics

Learn about electric potential concepts, Kelvin Water Dropper, signal generators, continuous charge distributions, and configuration energy in this physics class outline.

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Exploring Electric Potential and Signal Generation in Physics

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  1. Class 06: Outline • Hour 1: • Electric Potential • Hour 2: • Expt. 3: Signal Generator

  2. Last Time:Kelvin Water DropperDefinition of Potential

  3. Kelvin Water Dropper This device separates an ever increasing amount of positive and negative charge until we get a spark across the gap at the bottom. How?

  4. PRS Questions:How Does The Water Dropper Work?

  5. Potential & Energy Units: Joules/Coulomb = Volts Work done to move q from A to B: Joules

  6. Potential Of Point Charge Take V = 0 at r = ∞:

  7. Potential in Uniform Fields

  8. PRS Question:Point Charge Potential

  9. Potential Landscape Positive Charge Negative Charge

  10. Deriving E from V

  11. Deriving E from V A = (x,y,z), B=(x+Dx,y,z) Ex = Rate of change in V with y and z held constant

  12. Deriving E from V In three dimensions: which implies

  13. Deriving E from V Introducing the gradient (del) operator: Then E is:

  14. Equipotentials

  15. Topographic Maps

  16. Equipotential Curves All points on equipotential curve are at same potential. Each curve represented by V(x,y) = constant

  17. Direction of Electric Field E E is perpendicular to all equipotentials Constant E field Point Charge Electric dipole

  18. Properties of Equipotentials • E field lines point from high to low potential • E field lines perpendicular to equipotentials • Have no component along equipotential • No work to move along equipotential

  19. Introduction toExperiment #3:Signal Generator Introduction to instrumentation requiring a look ahead at physics

  20. Ohm’s Law: Voltage & Current • Voltages can be constant (battery) or time dependent (AC power) • Charges want to move – current (C/s) • Motion restricted – resistance (Ohms) • V = I R • It takes energy to move charges: • P = V I (J/C C/s = J/s = Watts)

  21. Experiment #3:Signal Generator

  22. Continuous Charge Distributions

  23. Electric Potential from Continuous Charge Distribution Continuous charge distribution: Potential at P is found by summing over all dq Scalar not Vector

  24. R Group Problem: Ring of Charge P on axis of ring of charge, x from center Radius R, total charge Q (evenly distributed) Find V at P. Then derive E from V.

  25. Configuration Energy

  26. Configuration Energy How much energy to put two charges as pictured? • First charge is free • Second charge sees first:

  27. Configuration Energy How much energy to put three charges as pictured? • Know how to do first two • Bring in third: Total configuration energy:

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