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Electrostatics

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History. The word electricity comes from the Greek elektron which means 'amber'. The 'amber effect' is what we call static electricity. History ... – PowerPoint PPT presentation

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Title: Electrostatics


1
Electrostatics
  • Nay, electrophun!!!

2
History
  • The word electricity comes from the Greek
    elektron which means amber.
  • The amber effect is what we call static
    electricity.

3
History
  • Ben Franklin made the arbitrary choice of calling
    one of the demo situations positive and one
    negative.
  • He also argued that when a certain amount of
    charge is produced on one body, an equal amount
    of the opposite charge is produced on the other
    body

4
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5
Charge Concepts
  • Opposite charges attract, like charges repel.
  • Law of Conservation of Charge
  • The net amount of electric charge produced in any
    process is zero. thanks Ben!!!
  • Symbol q, Q
  • Unit C, Coulomb

6
Elementary Particles
  • If an object has a
  • charge ? it has less electrons than normal
  • - charge ? it has more electrons than normal

7
Ions and Polarity
  • If an atom loses or gains valence electrons to
    become or - , that atom is now called an ion.
  • If a molecule, such as H2O, has a net positive
    charge on one side and negative charge on the
    other it is said to be polar

8
Why does
  • Chemistry work?
  • Physics!!!
  • The electrostatic forces between ions (within
    molecules) form bonds called ionic bondsall
    bonds are ionic others, like covalent, are to a
    much lesser degree so that you can ignore the
    ionic properties of that type of bond.

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10
Why does
  • Biology work?
  • Physics!!!
  • The intermolecular electrostatic forces between
    polar molecules make such things as the DNA
    double helix possible.

11
Types of materials
  • Conductor a material that transfers charge
    easily (ex. Metals).
  • Insulator a material that does not transfer
    charge easily (ex. Nonmetals)
  • Semiconductors somewhere between 1 2 (ex.
    Silicon, carbon, germanium).
  • Superconductors some metals become perfect
    conductors below certain temperatures

12
Ways to Charge
  • By Conduction contact occurs between charged
    object and neutral object.
  • Result two objects with same charge
  • By induction no contact occurs between charged
    object and neutral object.
  • Result two objects with opposite charge
  • Credit Card You may use Visa, Master Card, or
    American Express
  • Result Debt from high interest rates

13
Conduction
14
Induction
Polarization
15
Conduction or Induction
B
A
16
Lightning
Becomes very negative
Becomes very positive
17
Electric Force
  • AKA Coulombs Law
  • Using a torsion balance, Coulomb found that the
    electric force between two charges is
    proportional to the product of the two charges
    and inversely proportional to the square of the
    distance between the charges.

18
Electric Force
19
Electric Force
  • q ? charge, C
  • r ? distance between charges, m
  • FE ? Electric Force, N ? VECTOR
  • kc? coulomb constant, 8.99x109Nm2/C2

20
Coulomb Constant
21
Electric Field
  • The electric force is a field force, it applies
    force without touching (like the gravitational
    force)
  • In the region around a charged object, an
    Electric Field is said to exist

22
Electric Field
  • Rules for Drawing Electric Field Lines
  • The lines must originate on a positive charge (or
    infinity) and end on a negative charge (or
    infinity).
  • The number of lines drawn leaving a positive
    charge or approaching a negative charge is
    proportional to the magnitude of the charge.
  • No two field lines can cross each other.
  • The line must be perpendicular to the surface of
    the charge

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27
Ex 21.58 p 831 Signs Why E smallest, why
28
Electric Field
  • E ? electric field strength, N/C ? VECTOR
  • q0 ? test charge, C
  • q ? charge producing field, C
  • r ? distance between charges, m
  • FE ? Electric Force, N ? VECTOR
  • kc? coulomb constant, 8.99x109Nm2/C2

29
E-Field vs g-field
30
E-Field
31
E-Field Calculuspp 813 818
32
Conductors in Electrostatic Equilibrium
  • The electric field is zero everywhere inside a
    conductor.
  • Any excess charge on an isolated conductor
    resides entirely on the outside surface of the
    conductor.
  • The electric field just outside the charged
    conductor is perpendicular to the conductors
    surface.
  • On an irregularly shaped conductor, charge tends
    to accumulate where the radius of curvature is
    the smallest, i.e. AT SHARP POINTS.

33
Van der Graff Generator
34
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