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Phys chapter 20 notes

Phys chapter 20 notes - Chapter 20 Electric Potential and...

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Chapter 20: Electric Potential and Capacitance 1. The concepts covered in this chapter are: 1. Electric potential 2. Electric potential energy 3. Capacitance 4. Capacitors arranged in series and parallel configuration 5. Air- and dielectric-filled capacitors 6. Potential energy stored in capacitors 2. Potential and Potential Energy. In the previous chapter we learned that charges exert a force on each other according to Coulomb’s law. This means that such forces that occur among the charges can change a given configuration of charges: in the field view of electrostatic interaction the electric fields of various charges interact to make the charges move, i.e., the electric field does work on the charge configuration). The configuration can also be changed by an external agent, i.e., work can be performed by an external agent. This change in charge configuration will show up as a change in the potential energy of the system (the charge configuration). The change in the potential energy between (or of ) two charges is defined as Δ W field = − Δ W ext = Δ U …[1] Δ U ab = U a –U b = . b b a a . F dr q E dr = JK JJK JJKJJK …[2] The potential difference Δ V = V b - V a is defined as: V b - V a = . b a E dr JK JJK …[3] Potential can be defined as the potential energy per unit charge ( recall a similar definition of the electric field E as the force per unit charge, q E = F ) A point charge Q, creates an electric potential V(r) at a distance r from it given by: V(r) = kQ/r ( referenced to infinity, i.e., 0 ( ) V ∞ = ) …[4] 1
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