Physics for Scientists and Engineers 8ed - ch25 - PowerPoint Slides

# Physics for Scientists and Engineers 8ed - ch25 - PowerPoint Slides

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Chapter 25 Electric Potential

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Electrical Potential Energy When a test charge is placed in an electric field, it experiences a force The force is conservative If the test charge is moved in the field by some external agent, the work done by the field is the negative of the work done by the external agent is an infinitesimal displacement vector that is oriented tangent to a path through space o q = Φ Ε r r d s r
Electric Potential Energy, cont The work done by the electric field is As this work is done by the field, the potential energy of the charge-field system is changed by Δ U = For a finite displacement of the charge from A to B, B B A o A U U U q d = - = - Ε σ r r o d q d = Φ σ Ε σ r r r r o q d - Ε σ r r

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Electric Potential Energy, final Because the force is conservative, the line integral does not depend on the path taken by the charge This is the change in potential energy of the system
Electric Potential The potential energy per unit charge, U / q o , is the electric potential The potential is characteristic of the field only The potential energy is characteristic of the charge- field system The potential is independent of the value of q o The potential has a value at every point in an electric field The electric potential is o U V q =

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Electric Potential, cont. The potential is a scalar quantity Since energy is a scalar As a charged particle moves in an electric field, it will experience a change in potential B A o U V d q = = - Ε σ r r
Electric Potential, final The difference in potential is the meaningful quantity We often take the value of the potential to be zero at some convenient point in the field Electric potential is a scalar characteristic of an electric field, independent of any charges that may be placed in the field

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Work and Electric Potential Assume a charge moves in an electric field without any change in its kinetic energy The work performed on the charge is W = Δ U = q Δ V
Units 1 V = 1 J/C V is a volt It takes one joule of work to move a 1-coulomb charge through a potential difference of 1 volt In addition, 1 N/C = 1 V/m This indicates we can interpret the electric field as a measure of the rate of change with position of the electric potential

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Electron-Volts Another unit of energy that is commonly used in atomic and nuclear physics is the electron-volt One electron-volt is defined as the energy a charge-field system gains or loses when a charge of magnitude e (an electron or a proton) is moved through a potential difference of 1 volt 1 eV = 1.60 x 10 -19 J
Potential Difference in a Uniform Field The equations for electric potential can be simplified if the electric field is uniform: The negative sign indicates that the electric potential at point B is lower than at point A Electric field lines always point in the direction of decreasing electric potential B B B A A A V V V d E d Ed - = ∆ = - = - = - Ε σ σ r r

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## This note was uploaded on 05/22/2010 for the course PHYS 2326 taught by Professor Staff during the Summer '08 term at HCCS.

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Physics for Scientists and Engineers 8ed - ch25 - PowerPoint Slides

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