Electric Potential and

1
Overview of
Electric Potential and Potential Energy
2
Recall Gravitational PE

• The work done to lift a ball of mass 1 kg a
  vertical height of 1 m is 10 J
• What is the work done to lift 5 bowling balls?

3
Work done for total job vs. work done per ball

• The work done to lift one ball is 10 J, and the
  work done to lift five is 50 J. The work done
  per ball remains 10 J.

4
Electrical PE

• Assume that it takes 10 J to lift one positive
  charge up from a negative plate to a positive
  plate

• How much will it take to lift 5 charges from
  the negative plate to the positive plate?

5
Work done for total job vs. work done per charge

• The work done to lift one charge is 10 J, and the
  work done to lift five is 50 J. The work done
  per charge remains 10 J.
• The electrical PE is the total work done
• The electrical potential is the work done per
  charge (measured in J/C or volts (V))

6
Which is more dangerous?
150,000 C at 12 V
1 x 10-6 C at 300,000 V
7
Recall Gravitational PE

• When in a uniform field, Ugmgh
• In a changing field (such as around planet),

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Electrical Potential

• When in a uniform E-field, VW/qEd
• In a changing field (such as that around a point
  charge),

9
Adding potentials

• The total potential at a point near many point
  charges is the numerical sum of the contribution
  from each charge. Potential is NOT a vector.

10
Equipotential lines

• Equipotential lines are like the lines on a
  contour or topographic map they represent
  levels of constant potential

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Equipotential lines, cont.

• No work is done to move along an equipotential
  line or curve
• Equipotential lines (curves) are always
  perpendicular to E-field lines

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Relationship between E and V

• The magnitude of the E-field is given by the
  gradient of the potential