Chapter_4 - General Physics II Chapter 4: Electric...

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General Physics II Chapter 4: Electric Potential Introduction Electric Potential or Potential or Voltage is an important concept related to the electric field and to energy. In order to understand potential concept let ur summarize gravitational potential energy concept. Similarity between the gravitational force and the electrical force. Gaziantep University Faculty of Engineering Department of Engineering Physics 1 B − = = We know that the gravitational force is a conservative force, and we know that there is a gravitational potential energy associated with a mass placed in the gravitational field. And the change in the potential energy equals the negative of the work done by the conservative gravitational force. That is, ∆= BA A UU U W or, W B A B A U U In words, the work done by the conservative force moving the object from A to B equals the object’s initial potential energy minus the final potential energy. At the surface of the earth, the gravitational field points downward (the direction the gravitational force acts on objects). A B mg B A qE E g Suppose an object of mass m is moved from point A to point B in the gravitational field. Is the work done by gravity, W , positive or negative? And which point, A or B, represents a higher potential energy? B A Note that the equation that describes the electrical force has the same form as the gravitational force: 12 22 and mm qq FG Fk rr == , and and . constant Fm g constant Fq E Because the forces are analogous, we can conclude that the electrical force is also a conservative force and gives rise to a potential energy. This is called the electrical potential energy associated with a charge in an electric field. As we mentioned in the first chapter the difference between gravitational forces and energies and electrical forces and energies is that the mass in gravity is always positive , whereas the charge in electricity can be positive or negative . For a more general analysis, consider a charge q moving from point A to point B in the electric field shown. The work done by the electric field as the charge moves from A to B is written as () A BB A A B U UU UU =− = W =−∆ AB U U W −= Uq , y d B A y or, A B AA F dl q E dl = •= ∫∫ GG E d G A . This is the electric potential energy. Exercises 1. A uniform electric field E G p ints directly downward as in figure. o
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General Physics II Gaziantep University Faculty of Engineering Department of Engineering Physics 2 . What is the difference in the potential energies of a charge + q placed in positions A and B + q is released from rest at point A, at what velocity will it be traveling as it . A point charge + Q creates an electric field in space. f a charge + q between the positions A . At what point does the charge have a higher potential energy?
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Chapter_4 - General Physics II Chapter 4: Electric...

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