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Ch 20,21 Notes

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  1. 1. Electrostatics Ch 20
  2. 2. Electrostatics Study of electrical charges that can be collected and held in one place
  3. 3. Electrical Basics All atoms have a positively charged nucleus (made up of protons (+) and neutrons (0) that are surrounded by electrons (-)) When the positive charge equals the negative charge the atom is neutral Electrons can be removed or transferred by the addition of energy.
  4. 4. Conservation of Charge Electric charge is never created or destroyed, just transferred by the separation of positive and negative charge Like charges repel Opposite charges attract A neutral object will be attracted to a charged object
  5. 5. Electrical Materials Conductors – materials through which charges will move about easily because they have loosely bound electrons; Ex: most metals Insulators - materials through which charges will not move about easily because they have tightly bound electrons; Ex: glass, wood, plastic
  6. 6. Charging a neutral object Conduction – charging a neutral object by touching it with a charged object Induction – charging a neutral object without touching it, but by the separation of charges
  7. 7. Coulomb’s Law The electrical force between 2 charged objects varies directly with the product of the charges and inversely with the square of the distance between them F = kqq’ k = 9EE9 Nm2/C2 d2 A repulsive force is positive because both charges are alike An attractive force is negative because the charges are opposites
  8. 8. Electric Fields Ch 21
  9. 9. Electric Fields A charge creates an electric field in all directions The electric field intensity is the force per unit charge E = F/q units are N/C
  10. 10. Electric Field Lines  Provide a model for the electric field. The strength of the field is indicated by the spacing between lines. The closer the lines the stronger the field. The field always points away from the positive towards the negative charge.
  11. 11. Electric Potential Difference Change in Potential Energy per unit charge; this is often called voltage difference ΔV = ΔPE/q or ΔV = Work/q units are J/C = volts Also ΔV = Ed
  12. 12. Grounding  Eliminating the excess charge by touching a charged object to the earth (low voltage). The charge moves from higher potential to lower potential until they are equal.
  13. 13.  All charged objects are on the surface of a solid conductor Excess charge will move to the outer surface of a hollow conductor
  14. 14. Capacitor  Stores charge; made up of two oppositely charged conducting plates separated by an insulator  Capacitance – ratio of charge stored to potential difference C = q/V units are C/V = 1 Farad (F)
  15. 15. Millikan Experiment  He determined the charge of an electron to be 1.6 EE -19 C  Eq = mg