Transcript Ch 17: Electric Potential

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
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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
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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.