Distinguishing Electric Potential and Potential Energy

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Distinguishing Electric Potential and Potential
Energy
Electric Potential
 Property of the source
charges
 Present whether or not a
charged particle is there
to experience it
 Measured in J/C or V
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Electric Potential Energy
 Due to interaction of a
charged particle q with
the source charges
 Measured in joules J
Electric Potential and Conservation of Energy:
Charges in an Electric Field
Recall: conservation of energy (isolated system) the total energy of the system is constant; i.e.
the sum of the kinetic energy and the electric
potential energy must be the same at any two
points.
Kf + (Uelec)f = Ki + (Uelec)i
 In terms of the electric potential:
½ mvf2
+ qV f
=
½ mvi2
+ qVi
 Class discussion/handout: ΔK = -q ΔV
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Charged Particle Moving Through a Potential
Difference
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The Electron Volt
 In terms of energy: 1J = (1 V)(1 C)
 A commonly used unit of energy comes from this
relationship - the electron volt (eV)
1 eV = (1.60 x 10-19 C)(1 V) = 1.60 x 10-19 J
Units: (C)(V) = C(J/C) = J
 1 electron volt is the kinetic energy gained by an
electron (or proton) if it accelerates through a potential
difference of 1 volt.
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Potential of a Parallel-Plate Capacitor
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Graphical Representations of Electric Potential
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The Potential Inside a Parallel-Plate Capacitor
units?
Uelec
Q
V
 Ex 
x
q
0 A
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Electric Potential of a Point Charge
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Connecting Electric Potential and Field
 Work done opposite to the E-field on a q
W = ΔUelec = q
ΔV
▬►
 To move the q at constant speed, the magnitude of the
Fhand = Felec and Felec = q E
W = Felec Δd = q E Δd
 Relating energy and field: ΔV = q E Δd = E Δd
q
Strength of E-field:
E = ΔV
Δd
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SI units: 1 V/m
Connecting Potential and Field
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Potential and Field for Three Important Cases
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A Conductor in Electrostatic Equilibrium
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