PHY 2049: Physics II

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PHY 2049 Physics II

• Hopefully all homework problems have been
• solved. Please see me immediately after the
  class if there is still an issue.
• Tea and Cookies We meet on Wednesdays at 400PM
  for tea and cookies in room 2165.

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quiz

• The electric field at a distance of 10 cm from an
  isolated point particle with a charge of 210-9 C
  is
• A. 1.8N/C B. 180N/C C. 18N/C D. 1800N/C E. none
  of these

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Quiz 2

• An isolated charged point particle produces an
  electric field with magnitude E at a point 2m
  away from the charge. A point at which the field
  magnitude is E/4 is
• A. 1m away from the particle
• B. 0.5m away from the particle
• C. 2m away from the particle
• D. 4m away from the particle
• E. 8m away from the particle

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PHY 2049 Physics II

• Last week
• Coulombs law, Electric Field and Gauss theorem
• Today
• Electric Potential Energy and Electric Potentials
• Numerous cases

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Potential Energy and Potential

• Force gt work gt change in Kgt change in
  Potential energy
• ?U Uf Ui -W - ?K
• Work done is path independent.
• KU constant.

U k q1 q2/r interaction energy of two
charges. Sign matters
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PHY 2049 Physics II

• Electric Potential
• V U/q -W/q
• Units of Joules/coulomb volt
• 1 eV e x 1V 1.6 x 10-19 J
• Also
• V kq/r
• Vf Vi -?E.ds
• In case of multiple charges, add as a number

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PHY 2049 Physics II

1. Neg., lower
2. ?
3. Pos., higher
4. Neg., higher
5. Pos., higher

Can you tell the sign of the charge by looking at
its behavior over a surface of potentials. Is
the speed at the end bigger or smaller than in
the beginning.
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PHY 2049 Physics II

• Vf-Vi -? k q/r2 dr
• Choose Vi V (8)0
• V(r) kq/r

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• V kpcos?/r2
• E -?V/?s -
• Uniformly charged disk
• V ??

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