p240_ct6_w12_jan_24 - Physics 240 Winter 2012 Lecture #6 My...

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Physics 240 Winter 2012 Lecture #6 Dr. Dave Winn 2405 Randall Lab winn@umich.edu My Office Hours (1416 Randall Lab) Monday 1pm-3pm Tuesday 1pm-3pm Thursday 2pm-4pm (Prof. Gidley) Learning Assistant Office Hours Tuesday 4-8pm Thursday 4-6pm Also in chat room Tue/Thu evening!
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When a positive charge moves in the direction of the electric field, A. the field does positive work on it and the potential energy increases. B. the field does positive work on it and the potential energy decreases. C. the field does negative work on it and the potential energy increases. D. the field does negative work on it and the potential energy decreases. Q23.1 + q E Motion E
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When a negative charge moves in the direction of the electric field, A. the field does positive work on it and the potential energy increases. B. the field does positive work on it and the potential energy decreases. C. the field does negative work on it and the potential energy increases. D. the field does negative work on it and the potential energy decreases. Q23.3 q E Motion E
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Consider a point P in space where the electric potential is zero. Which statement is correct? Q23.9 A. A point charge placed at P would feel no electric force. B. The electric field at points around P is directed toward P. C. The electric field at points around P is directed away from P. D. none of the above E. not enough information given to decide Only *Change* in potential matters. If you only know the potential at one point you don’t know anything at all…
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One more key idea in electrostatics • We have seen electrostatic force and developed the idea of electric field to quantify it • What about energy? Clearly there is energy stored in separated electric charge, it can come out as light and sound in a spark…
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Review of potential energy Work changes energy: W= F d x = KE For conservative forces work is reversible; they can take energy away and completely return it Recall PE definition: PE = -W conservative Neg. work by force increases PE, decreases KE Pos. work decreases PE, increases KE Cedar Point Millennium Force Ride… Examples
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Work done by gravity: Since force acts only downward, PE depends only on change in height h As objects move higher, energy is ‘stored’ as gravitational potential energy.   h
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p240_ct6_w12_jan_24 - Physics 240 Winter 2012 Lecture #6 My...

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