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

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

Electrical PE n Assume that it takes 10 J to lift one positive charge “up” from a negative plate to a positive plate n How much will it take to “lift” 5 charges from the negative plate to the positive plate?

Work done for total job vs. work done per charge n 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. n The electrical PE is the total work done n The electrical potential is the work done per charge (measured in J/C or volts (V))

Which is more dangerous? 1 x C at 300,000 V 150,000 C at 12 V

Recall: Gravitational PE n When in a uniform field, U g =mgh n In a changing field (such as around planet),

Electrical Potential n When in a uniform E-field, V=W/q=Ed n In a changing field (such as that around a point charge),

Adding potentials n 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.

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

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

Relationship between E and V n The magnitude of the E-field is given by the gradient of the potential