Physics 212 lecture 6: More on Electric Potential

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Physics 212 lecture 6 More on Electric
Potential

• Electric Potential Due to Continuous Charge
  Distributions
• Add up effects from many charges
• If for one charge
• And for an infinitesimal charge
• Then for a charge distribution

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Electric Potential Due to Charged Conductor
For any two points in equilibrium on the surface
of a conductor

• Why? Outward direction of E is ? to ds
  everywhere on surface.
•  
• Therefore a conductor in equilibrium is an
  equipotential surface
• V inside conductor is constant and to value on
  surface
• E inside conductor is zero everywhere
• E on surface of conductor is
• smaller where flatter
• large where there is greater curvature or a sharp
  point

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Obtaining Electric Field Given Electric Potential
Ex uniform E in 1-D Ex E from point
charge
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Questions for Groups

• Explain why equipotential surfaces are always
  perpendicular to electric field lines.
• Explain why, under static conditions, all points
  in a conductor must be at the same electric
  potential.
• Why should one avoid sharp points on conductors
  for high voltage equipment?
• How would your shield an electric circuit or
  laboratory from stray electric fields? Why does
  this work?

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Example Ch 25 43Rod of length L on x axis
with ??x where ? is a constant.a) units of
??b) Find V at a distance d on x-axis.
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Example Ch 25 49Spherical conductor has
R14cm and q26 ?C. Find E and V at r10, 20,
and 14 cm.
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Example Ch 25 37 Vabx between 0 and 6
meters. Where a 10V and b -7V/m.a) Find V
at x 0, 3, and 6m.B) Find mag and dir of E at
x0, 3, and 6m.