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Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
Columbs law pp
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Columbs law pp

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Transcript

  • 1. The Electrostatic Force • Charge of objects • And separation distance – Influence the force between them.
  • 2. As q increases, F increases.
  • 3. As D increases, F decreases. Distance Force
  • 4. Coulomb’s Law • Notice that d is squared!!!!!! This is another example of an inverse-square law. 1 2 2 c elec k q q F d = q charge (Coulombs or C) Distance (meter of m) Electric Force (Newtons or N) kc (8.99 x 109 N-m2 /C2 )
  • 5. Symmetries • Recall Newton’s Law of Gravitation: • And Coulomb’s Law: • Notice the similarities?? 1 2 2 c elec k q q F d = 1 2 2grav Gm m F d =
  • 6. Proportionality Constants • Notice their relative size!!! 1020 difference! 1 2 2 c elec k q q F d = 1 2 2grav Gm m F d = G (6.67 x 10-11 N-m2 /kg2 ) was a proportionality constant Newton’s Law of Universal Gravitation kc (8.99 x 109 N-m2 /C2 ) is the proportionality constant Coulomb’s Law
  • 7. Using Coulomb’s Law • Why do they use such small numbers for ordinary objects? Wouldn’t it make more sense to call them 1 C instead?? • The answer lies in the famous “Oil Drop Experiment.”
  • 8. Using Coulomb’s Law • So what sort of charges are we talking about? q is 1-10 C VERY LARGE q is more like 10-6 or 10-9 C
  • 9. The Elementary Charge • http://webphysics.davidson.edu/applets/pqp_preview/contents/pqp_errata/c d_errata_fixes/section4_5.html
  • 10. The Elementary Charge • Robert Millikan -1909 – electric charge is quantized. • Quantized - things can only have certain values, not just any value. • Ex. Is it possible to own 2 ½ bicycles??? • Animation 1 (Quicktime) • Animation 2 (Java)
  • 11. The Elementary Charge • Millikan demonstrated that all the oil droplets had charges which were multiples of each other! • All the droplets carried some multiple of what is called the Elementary Charge, 1.6 x 10-19 Coulombs. • This is the charge of a single proton or electron. • Ordinary objects have charges like 10-9 C, this is still about 10 billion excess charges!!!
  • 12. Using Coulomb’s Law • Why is Coulomb’s Law called an “inverse- square law?” • Because of the d2 in the equation. • Doubling the distance between objects cuts the force by ¼ , just like Newton’s Universal Law of Gravitation. • Ex. Sound intensity, Spray paint, the “Butter Gun”
  • 13. The Inverse-Square Butter Gun
  • 14. Bohr’s Model of Hydrogen • You’ve seen the similarities between Newon’s U.L.o.G. and Coulomb’s Law. Niels Bohr used this similarity to create a model of the Hydrogen atom. • Just like the Earth orbiting the Sun, Bohr pictured the electron orbiting the proton. • Animation

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