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Charge

Charge. Feb 17, 2014. Warm Up – Reading Quiz 3 minutes!!. Like charges _______ and opposite charges _____. Protons have a ______ charge and electrons have a _________ charge. In a closed system, charge is ___________.

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Charge

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  1. Charge Feb 17, 2014

  2. Warm Up – Reading Quiz3 minutes!! • Like charges _______ and opposite charges _____. • Protons have a ______ charge and electrons have a _________ charge. • In a closed system, charge is ___________. Keep your pencil out, you’ll be taking notes today. Notes pages are on the lab table.

  3. Turn them in! • One person per table group • You have 45 seconds to have them in to the folder • Be ready to take notes (pages provided!)

  4. Charge is a property of matter • Matter is made of atoms and electric charge is a property of the particles inside every atom. • That means on a very fundamental level, similar to mass, electric charge is a basic property of matter. • Mass can only be zero or positive. (Even antimatter has positive mass!) Electric charge, on the other hand, can be positive, negative, or zero (neutral).

  5. Structure of an atom • A complete atom has an equal number of protons and electrons, therefore a whole atom has zero net electric charge.

  6. Coulomb • The unit of electric charge • Notated as “C” • In honor of Charles-Augustin de Coulomb, a French physicist who made the first accurate measurements of electric force • 1 Coulomb is A LOT of charge • 6×1018electrons • Ordinary static electricity results from an excess charge of less than one millionth of a coulomb • A lightning bolt is approximately 10 C of charge

  7. Net Charge • Your body is full of electric charges. Not just a few, but many—around 1029! • Your body is electrically neutral, which means that it has no excess of either positive or negative charge. In physics terms, your body has no net charge.

  8. Insulators and Conductors Insulators Conductors Relatively low resistance to flow of electric current Atomic electrons able to flow within the material (Iike a fluid) Most metals Copper Aluminum Gold • Poor conductor of electric current • Atomic electrons bound to the atom within the material • Rubber, plastic, glass, silk • Semiconductors: added impurities allow for conduction (like silicon)

  9. Methods of Charging • Friction • Induction • Polarization • Conduction • Grounding

  10. Friction • Remember the atomic energy levels? • When an electron gained enough energy, the atom could be “ionized” • So where did that electron go? • It became free to cause a net charge somewhere else!

  11. What affects charging by friction? • Humidity • Ions in the air can “steal” the free electrons • Materials • Triboelectric series • Contact area • Effects are local for insulators

  12. Dr. Jason Hafner

  13. Induction • Example: Positively charged object brought near an uncharged conductor • Electrons in conductor: “run away!” • Charges become rearranged • Works with negative charged objects too…

  14. Polarization, Induction, Conduction

  15. Polarization and Induction • Neutral object • Conductor: polarization of object • Insulator: polarization of atoms/molecules

  16. Conduction • When a charged object touches another • Electrons move to spread out as much as possible

  17. Electroscope • Uses electrostatic induction to detect electric charge

  18. Grounding • When a conductor is connected to Earth by a wire or other method • A charged conductor will lose its net charge (will gain or lose electrons to become neutral) • A polarized conductor will gain a net charge after being grounded

  19. Grounding

  20. Van de Graaff generator • Usually positively-charged dome (BUT not always!)

  21. Summary • Positive and negative charges • Unit is Coulombs (C) • Insulators vs. Conductors • 5 ways of charging an object • Homework: Read handout on electric fields

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