SM_chapter25

# SM_chapter25 - 25 Electric Potential CHAPTER OUTLINE 25.1...

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25 Electric Potential CHAPTER OUTLINE 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 25.8 Application of Electrostatics ANSWERS TO QUESTIONS Q25.1 When one object B with electric charge is immersed in the electric f eld oF another charge or charges A , the system possesses electric potential energy. The energy can be measured by seeing how much work the f eld does on the charge B as it moves to a reFerence location. We choose not to visualize A ’s eFFect on B as an action-at-a- distance, but as the result oF a two-step process: Charge A creates electric potential throughout the surrounding space. Then the potential acts on B to inject the system with energy. *Q25.2 (i) The particle Feels an electric Force in the negative x direction. An outside agent pushes it uphill against this Force, increasing the potential energy. Answer (a). (ii) The potential decreases in the direction oF the electric f eld. Answer (c). *Q25.3 The potential is decreasing toward the bottom oF the page, so the electric f eld is downward. Answer (F). *Q25.4 (i) At points oFF the x axis the electric f eld has a nonzero y component. At points on the negative x axis the f eld is to the right and positive. At points to the right oF x = 500 mm the f eld is to the leFt and nonzero. The f eld is zero at one point between x = 250 mm and x = 500 mm. Answer (b). (ii) The electric potential is negative at this and at all points. Answer (c). (iii) Answer (d). (iv) Answer (d). Q25.5 To move like charges together From an inf nite separation, at which the potential energy oF the system oF two charges is zero, requires work to be done on the system by an outside agent. Hence energy is stored, and potential energy is positive. As charges with opposite signs move together From an inf nite separation, energy is released, and the potential energy oF the set oF charges becomes negative. Q25.6 (a) The equipotential surFaces are nesting coaxial cylinders around an inf nite line oF charge. (b) The equipotential surFaces are nesting concentric spheres around a uniFormly charged sphere. *Q25.7 Answer (b). The potential could have any value. *Q25.8 The same charges at the same distance away create the same contribution to the total potential. Answer (b). 49

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50 Chapter 25 *Q25.9 The change in kinetic energy is the negative of the change in electric potential energy, so we work out q V = q ( V f V i ) in each case. (a) ( e )(60 V 40 V) = +20 eV (b) ( e )(20 V 40 V) = 20 eV (c) ( e )(20 V 40 V) = +20 eV (d) ( e )(10 V 40 V) = +30 eV (e) ( 2 e )(50 V 40 V) = +20 eV (f) ( 2 e )(60 V 40 V) = +40 eV With also (g) 0 and (h) +10 eV, the ranking is f > d > c = e = a > h > g > b.
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SM_chapter25 - 25 Electric Potential CHAPTER OUTLINE 25.1...

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