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Transcript
Ch 17: Electric Potential Ch 17 introduces the idea of electric potential (also called Voltage) Electric Potential • Ch 17 looks at Electricity in terms of the ENERGY stored or available. • Remember we looked at mechanics in terms of Forces and then Energy. • Now we look at static electricity in terms of Forces (ch 16) and now Energy (ch 17). Electric Potential • Recall that change in Potential Energy = Work done by a conservative force. • We did this for gravitational PE. • Now we look at this same idea in terms of electrical stored energy • There is stored electrical energy because there is an electric force. Electric Potential • • • • Recall E = F/q = electric Field So F = Eq W = Fd = Eqd = -change in U As charge moves through the electric field it loses electric potential energy U and gains Kinetic Energy. Energy is conserved, yes?! Electric Potential • Electric Potential is defined as the electric potential energy (U) per charge (q) • Or V = U/q • Voltage tells you how much energy there is per charge, measured in Joules per Coulomb. Relation between Electric Potenial and Electric Field • • • • • W/q = -U/q = Voltage W = -qV But W = Fd where F = Eq So W = Eqd = qV results in V = Ed V = Ed is the relationship between Voltage and Electric Field when the electric Field is uniform like between 2 parallel plates 17-4 The Electron Volt is a Unit of Energy • When dealing with small amounts of charge, a Joule is a lot of energy. • The Electron Volt is a unit of energy….it’s the energy required to move one electron thru a 1 Volt potential. • 1 eV = qV =(1.6 x 10-19C)(1V)= 1.6 x 10-19J 17-5 Electric Potential Due to Point Charges • Using the idea that the electric potential is zero at infinity, “it can be shown” that…. • V = kQ/r This is the electric potential from a point source Q at some distance r.