Electrostatics

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Electrostatics

• AP Summer Institute in Physics

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Electrostatics Relationships

• Kids want to memorize disconnected formulas.
• The physics very similar to mechanics can be
  emphasized by focusing on links between
  equations.
• This approach emphasizes fundamental
  relationships and reduces the need for
  memorization.

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Coulombs Law has two forms

• Constants in both forms are different.
• Coulombs law applies directly only to
  spherically symmetric charges.

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Spherically Symmetric Forces

• Newtons Law of Gravity
• Coulombs Law

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• Sample Problem Calculate the mass of ball B,
  which is suspended in midair.

qA 1.50 nC
A
1.3 m
B
qB -0.50 nC
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• Sample Problem What is the charge on the bead?
  Its mass is 32 mg.

E 5000 N/C
40o
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Sample Problem

• What is the force on the 4 mC charge?

y (m)
2.0
-3 mC
1.0
2 mC
4 mC
2.0
1.0
x (m)
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Electric Field

• charge

• - charge

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Electric Field

• dipole ( and charge)

• 2 charges

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Electric Field in Capacitor
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• Sample Problem A particle bearing 10.0 mC is
  placed at the origin, and a particle bearing 5.0
  mC is placed at 1.0 m. Where is the field zero?

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• Sample Problem A 3.0 µC charge is moved through
  a potential difference of 640 V. What is its
  potential energy change?

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• Sample Problem An electric field is parallel to
  the x-axis. What is its magnitude and direction
  if the potential difference between x 1.0 m and
  x 2.5 m is found to be 900 V?

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• Sample Problem What is the voltmeter reading
  between A and B? Between A and C? Assume that the
  electric field has a magnitude of 400 N/m.

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• Sample Problem How much work would be done BY
  THE ELECTRIC FIELD in moving a 2 mC charge from A
  to C? From A to B? from B to C?. How much work
  would be done my an external force in each case?

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• Sample Problem If a proton is accelerated
  through a potential difference of -2,000 V, what
  is its change in potential energy?
• How fast will this proton be moving if it started
  at rest?

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• Sample Problem How much work was done in
  assembling the charge configuration shown below?