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Electrostatics

Electrostatics. The Atom. All matter is composed of atoms that contain: Protons (positively charged particles) Neutrons (neutrally charge particles) Electrons (negatively charged particles). Every atom has a positively charged nucleus surrounded by negatively charged electrons.

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Electrostatics

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  1. Electrostatics

  2. The Atom • All matter is composed of atoms that contain: • Protons (positively charged particles) • Neutrons (neutrally charge particles) • Electrons (negatively charged particles) Every atom has a positively charged nucleus surrounded by negatively charged electrons.

  3. Electric charge, “q”, is measured in Coulombs, C. • All electrons are identical in mass and quantity of charge : q = - 1.6 x 10-19 C • All protons are identical to other protons and although they are more massive than electrons, they have the same quantity of positive charge as electrons have negative charge: q = + 1.6 x 10-19 C Compare the mass difference!

  4. Electrical forces explain bonding in molecules. • All neutrons are identical to other neutrons, have more mass than protons, and have neither positive or negative charge. • Atoms typically have the same number of protons as electrons so the atom has a net charge of zero. • When an atom has lost or gained electrons, it is charged and called an ION.

  5. Charles Coulomb, mid 1700’s, studied and published papers about the electrostatic force between 2 charged objects.

  6. The fundamental rule of electricity: Like charges repel; opposites attract. A neutral object will attract both positive and negative charges

  7. Hmmm.. + + + - - - Ben Franklin was the first to use the terms “positive” and “negative” to describe electrical charge. Mid 1700’s

  8. Coulomb’s Law calculates the electrical force between charges: where k is a constant, k = 9 x 109 N·m2/C2

  9. Sample problem using the formula • sample problem • Physics Classroom website

  10. Sample Problems using logic • The electrostatic force between two charges located 2 meters apart is 0.10 N. What will the force between these charges when they are located 1 meter apart? Solution: The distance has halved.The force will become stronger if the charges are closer. • To get the factor, put ½ in place of d in the denominator (remember to square it). F ≈ 1/d2 • 1/(1/2)2 = 1/(1/4) = 4; now multiply the original force times the factor • (.10)(4) = .40N

  11. A 2-C charge and a 4-C charge attract each other with 10 N of force. How much will a 2-C charge and an 8-C charge attract each other when placed the same distance apart? • Solution: one of the charges doubled. The force will be stronger since force and charge are directly related. • The force will double: 10 N X 2 = 20 N

  12. The charge on an electron is 1.6 x 10-19 C. How many electrons make a charge of 4.0C? • Set up a proportion!! • 1 e- = ??? e-

  13. Number of electrons, e - • I want to know how many electrons are in a lightning bolt that transfers 20 Coulombs of charge. • I know the number of Coulombs for 1 e – is equal to 1.6 X 10 -19 C. I can set up a proportion, cross-multiply and divide. • 1 e – = ? e – 20 X 1 / 1.6 X 10 -19 • 1.6 X 10 -19C 20 C = 1.25 X 10 -20 • That’s a lot of electrons!!!

  14. Conductors • have easily moveable electric charges • Many are metals that have “free electrons” • Positive ions may also be mobile Insulators • Charges cannot move easily • Examples: plastic, wood, glass http://www.physicsclassroom.com/Class/estatics/u8l1d.cfm

  15. Semiconductor -Conductivity is between conductors and insulators unlike metals, they can conduct more efficiently with temperature increase used in computers Superconductor: NO resistance to the flow of electrons. So far, no material is a superconductor except at extremely low temperatures.

  16. Water: insulator or conductor? • PURE water does NOT conduct electricity • Bath water (or water from the tap) often has impurities or ions that allow conduction • The purer the water, the lower the conductivity • (the conduction of electricity is called ELECTROLYTIC behavior- ) • Air: insulator or conductor? • Usually an insulator, thankfully • When strong forces are present, electron’s can be stripped from air molecules, creating ions • example: lightning

  17. Lightning An electrical discharge between the clouds and the ground or between two clouds. Ions in the air react to form high heat plasma, producing an expansion: a flash we see as lightning and the boom we hear as thunder!!

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