Ch 17: Electric Potential

1. Ch 17: Electric Potential Ch 17 introduces the idea of electric potential (also called Voltage)

2. 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).

3. 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.

4. 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?!

5. 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.

6. 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

7. 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

8. 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.