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# Jan21Note - PHYS142 Lecture 7 Electric Potential Chapter 25...

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Electric Potential • Chapter 25 All sections except 8 25.1 Electric Potential and Potential Difference 25.2 Potential Difference in a Uniform Electric Field 25.3 Electric Potential and Potential Energy Due to Point Charges 25.4 Obtaining the Value of the Electric Field from the Electric Potential 25.5 Electric Potential Due to Continuous Charge Distributions 25.6 Electric Potential Due to a Charged Conductor 25.7 The Millikan Oil-Drop Experiment 2 PHYS142 Lecture 7

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3 Change in the potential energy when a charge q 0 moves from A to B in electric field, E , A B q o E Electric potential energy A B B A U U s d E q U 0 Similar to the E-field, a property due to the presence of a charge, the electric potential at a point is defined as the electric potential energy per unit charge : Electric potential The potential is a scalar quantity. A B B A V V s d E q U V q U V , Units: (J/C). also Volt (V)
Two points A and B are located within a region in which there is an electric field. How would you describe the potential difference Δ V = V B − V A ? Quick quiz 25.1 i) 1 2 3 0% 0% 0% 1. It is positive. 2. It is negative. 3. It is zero.

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Two points A and B are located within a region in which there is an electric field. A negative charge is placed at A and then moved to B. How would you describe the change in potential energy of the charge-field system for this process? Quick quiz 25.1 ii) 1 2 3 0% 0% 0% 1. It is positive. 2. It is negative. 3. It is zero.
Potential difference in a uniform E-field (25.2) B A B A s d E s d E q q q U V 1 A B q E d If E is uniform (constant), then: B A Ed s d E V minus sign indicates decrease in potential. Similar to the gravitational case where the gravitational potential and potential energy decreases when an object is moved in the direction of the gravitational field. However, unlike the mass, the charge can be positive or negative . 6

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If a positive charge is moved from A to B, qEd V q U and the potential energy is lowered. Work is done by the E-field.
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## This note was uploaded on 02/22/2011 for the course PHYS 142 taught by Professor Altounian during the Spring '07 term at McGill.

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Jan21Note - PHYS142 Lecture 7 Electric Potential Chapter 25...

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