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ELECTRIC FORCES AND ELECTRIC FIELDS

ELECTRIC FORCES AND ELECTRIC FIELDS. CHAPTER 18. 18.1 The Origin of Electricity. Electric nature comes from the atomic structure. Electric charge : intrinsic property of protons and electrons, and only two types of charge have been discovered. + - Proton: + Electron: - Neutron: o.

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ELECTRIC FORCES AND ELECTRIC FIELDS

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  1. ELECTRIC FORCES AND ELECTRIC FIELDS CHAPTER 18

  2. 18.1 The Origin of Electricity • Electric nature comes from the atomic structure. • Electriccharge: intrinsic property of protons and electrons, and only two types of charge have been discovered. + - • Proton: + • Electron: - • Neutron: o

  3. SI UNIT FOR MEASURING THE MAGNITUDE OF AN ELECTRIC CHARGE IS THE COULOMB (C). • e = 1.60 x 10^-19 C • e = electric charge, could be positive or negative. • In nature atoms will be neutral, same number of protons and neutrons. • Electricallyneutral: when an atom, or any object, carries no net charge.

  4. Charge on an electron or proton is the smallest amount of free charge that has been discovered. • Charges of larger magnitude are built up on an object by adding or removing –e. • Any charge of magnitude q is an interger multiple of e. • q = Ne • N = interger • e = electric charge Electric charge is said to be quantized.

  5. Example 1: A Lot of Electrons • How many electrons are there in one coulomb of negative charge? • The negative charge is due to the presence of excess –e, since they carry a – charge. Because an electron has a charge whose magnitude is e = 1.60 x 10^-19 C, the number of –e is equal to the charge q divided by the charge e on each electron.

  6. 18.2 Charged Objects and The Electric Force • Electrons can be transferred. • Object that gains e- will have a negative charge. • Object that gives e- will have a positive charge. • Separation of charge occurs often when two unlike materials are rubbed together.

  7. Law of Conservation of Electric Charge • Electric charges are useful in chemical rxns. Electric circuits, and radioactive decay. LAW OF CONSERVATION OF ELECTRIC CHARGE During an process, the net electric charge of an isolated system remains constant (is conserved).

  8. Like charges repel and unlike charges attract each other • Electric force: (electrostatic force) can alter the motion of an object. • F = ma -contributes to the net external force. • Pop can demo

  9. Electronic Ink • http://www.youtube.com/watch?v=3n2xxqMQyfY&feature=related • http://www.youtube.com/watch?v=4F3mHz0xEDs&NR=1&feature=fvwp • Watch: http://www.seikowatches.com/baselworld/2007/press/details/070412_11.html

  10. Review q = magnitude of charge e = charge of an electron = 1.60 x 10^-19 C N = number of electrons

  11. Practice Problems 1.

  12. Practice Problem 3.

  13. 18.3 Conductors and Insulators

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