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- 1. Electrostatics
- 2. <ul><li>Charge is the total balance between electrons and protons </li></ul><ul><ul><li>Charge is conserved </li></ul></ul><ul><li>Conductors easily allow the flow of electricity, insulators prevent it </li></ul>
- 3. Static Electricity; Electric Charge and Its Conservation Charge comes in two types, positive and negative; like charges repel and opposite charges attract
- 4. Static Electricity; Electric Charge and Its Conservation Electric charge is conserved – the arithmetic sum of the total charge cannot change in any interaction.
- 5. Electric Charge in the Atom Atom: Nucleus (small, massive, positive charge) Electron cloud (large, very low density, negative charge)
- 6. Electric Charge in the Atom Atom is electrically neutral. Rubbing charges objects by moving electrons from one to the other.
- 7. Electric Charge in the Atom Polar molecule: neutral overall, but charge not evenly distributed
- 8. Insulators and Conductors Conductor: Charge flows freely Metals Insulator: Almost no charge flows Most other materials Some materials are semiconductors.
- 9. Metal objects can be charged by conduction:
- 10. They can also be charged by induction:
- 11. 16.4 Induced Charge; the Electroscope Nonconductors won’t become charged by conduction or induction, but will experience charge separation:
- 12. Induced Charge; the Electroscope The electroscope can be used for detecting charge:
- 13. Induced Charge; the Electroscope The electroscope can be charged either by conduction or by induction.
- 14. Induced Charge; the Electroscope The charged electroscope can then be used to determine the sign of an unknown charge.
- 15. Summary <ul><li>4 ways to change the charge of an object </li></ul><ul><ul><li>Friction – friction causes some atoms to lose electrons, creating a negative charge </li></ul></ul><ul><ul><li>Induction – The use of an outside charge polarizes the objects </li></ul></ul><ul><ul><li>Conduction – Touching the two objects transfers charge </li></ul></ul><ul><ul><li>Grounding – Charge is moved to a large object </li></ul></ul>
- 16. Coulomb’s Law Experiment shows that the electric force between two charges is proportional to the product of the charges and inversely proportional to the distance between them.
- 17. Coulomb’s Law Coulomb’s law: (16-1) This equation gives the magnitude of the force.
- 18. Coulomb’s Law The force is along the line connecting the charges, and is attractive if the charges are opposite, and repulsive if they are the same.
- 19. Coulomb’s Law Unit of charge: coulomb, C The proportionality constant in Coulomb’s law is then: Charges produced by rubbing are typically around a microcoulomb:
- 20. Coulomb’s Law Charge on the electron: Electric charge is quantized in units of the electron charge.
- 21. Coulomb’s Law The proportionality constant k can also be written in terms of , the permittivity of free space: (16-2)
- 22. Coulomb’s Law Coulomb’s law strictly applies only to point charges. Superposition: for multiple point charges, the forces on each charge from every other charge can be calculated and then added as vectors.
- 23. Solving Problems Involving Coulomb’s Law and Vectors The net force on a charge is the vector sum of all the forces acting on it.
- 24. <ul><li>2 electrons are placed 2 x 10 -9 m apart. What is the force each electrons applies to the other? </li></ul><ul><ul><li>Force must be equal </li></ul></ul><ul><ul><li>Concept of net force is the same </li></ul></ul>
- 25. <ul><li>To the previous problem we add a proton 1 x 10 -9 to the left of the electrons. With what force, and in which direction will the middle electron move? </li></ul>

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