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Lecture_08_(Chap.17)

# Lecture_08_(Chap.17) - Announcements Exam 1 on Feb...

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Announcements Exam 1 on Feb 15 (Tuesday), 8-9:30 PM, PHYS 202,203 Covers materials from Chap.14 – 17. Practice exam is posted on the course home page. 1

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() xyz VE l E x E y E z  we multiply through by we recover the relation between If we multiply through by q , we recover the relation between the change in potential energy and work done on q by the internal force. 2
Example 30 0 o cos 100 (N/C) 2 (m) cos(30 ) 173 volts VE l E l   3

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Sign of the Potential Difference U el q V The potential difference V can be positive or negative. The sign determines whether a particular charged particle will gain r lose energy in moving from one place to another If q V < 0 – then potential energy decreases and K increases or lose energy in moving from one place to another. If q V > 0 – then potential energy increases and K decreases Path going in the direction of E : Potential is decreasing ( V < 0) Path going opposite to E : Potential is increasing ( V > 0) Path going perpendicular to E: Potential does not change ( V = 0) 4
Question A system consists of a proton inside of a capacitor. The proton moves from left to right as shown at a constant velocity due to the action of an external agent. Which of the following statement is true? V A) The proton’s potential energy is unchanged and the external agent does no work on the system. ) he proton’s potential energy decreases and the V 1 < V 2 B) The proton s potential energy decreases and the external agent does work W > 0 on the system. C) The proton’s potential energy decreases and the external agent does work W < 0 on the system. D) The proton’s potential energy increases and the external agent does work W < 0 on the system. E) The proton’s potential energy increases and the external agent does work W > 0 on the system. 5

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Sign of the Potential Difference U el q V If freed, a positive charge will move to the area with a lower potential : V f – V i < 0 0 V q U el 0 el U K (no external forces) V V 1 < V 2 Moving in the direction of E means that potential is decreasing 6
Sign of the Potential Difference U el q V o move a ositive charge the To move a positive charge to the area with higher potential : V f – V i > 0 0 V q U el V Need external force to perform work V 1 < V 2 Moving opposite to E means that potential is increasing 7

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Potential Difference in a on niform Field Non-uniform Field C x V = - <E x , E y , E z >   x   y   z From A to C: V 1 = -E 1x (x C
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Lecture_08_(Chap.17) - Announcements Exam 1 on Feb...

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