The Electric Field

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The Electric Field
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The electric field E at a point in space is
defined as an electric force F, acting on a
positive test charge q divided by the magnitude
of the test charge
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Units of Electric Field
1 N/C
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Superposition Principlefor Electric Fields
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Field Lines
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• At every point of electric field line, electric
  field E is tangent to this line. No two field
  lines can cross!
• The line must begin at positive charge and
  terminate on the negative one unless go to
  infinity.
• The number of line per unit area is proportional
  to the magnitude of electric field.

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Electric Fields and Conductors
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Important electric field inside of good
conductor is zero!!!!
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Important any net charge on a good conductor
distributes itself on the surface!!!!
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Electric field is always perpendicular to the
surface of conductor
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Conceptual Example
A hollow metal box is placed between two parallel
charged plates. Whats the field like inside the
box?
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P
d
d
q
Q
Is it possible to place a charge at point Q such
that the electric field produced at point P by
the two charges will be add to zero?
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• Two positive charges are a fixed distance apart.
  The sum of their charges is QT. What charge must
  each have in order
• Maximize the electric force
• Minimize it.