Download Ch 29 : Electric Potential and Electric Potential Energy

Ch 29 : Electric Potential and
Electric Potential Energy
Ch 29 defines electric potential
(Voltage) and potential energy (these
are 2 different terms and mean
different things)
Electric Field and Electric
Potential
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Remember this……..
Electric Field involves the idea of
Electric Force, where Electric Potential
involves the idea of Electric Energy
Electric Potential
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The electric field allows us to understand
something about electricity by looking at
electric forces and how a charge exerts a
force on another charge.
The electric potential is looking at
electricity in terms of energy.
The analogy is looking at Newtonian
mechanics in terms of Forces or in terms of
energy.
Ch 29.1
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Electric Potential Energy
Connection with mechanical energy
Change in U = -work done by a
conservative force.
Ugrav = mgh = potential energy of a
system of objects
If force is not constant W = ∫Fds
Ch 29.2 Potential energy of
point charges
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Using the idea that the work done equals the
negative change in potential energy, can
derive the change in U between 2 point
charges.
U = -W = ∫Fdx = ∫kq1q2/r2dx
U = kq1q2/r = electric potential energy
between point charges
U = positive if charges are the same and
negative if they are opposites
Electric Potential energy between
plates (uniform electric field
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Between plates there is a constant
Electric Field E = F/q
The work done in moving a charge
between the plates is W = Fd =Eqd
So the change in potential energy
between the plates is U = qEd where d
= the distance between the plates.
29.4 Electric Potential
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Electric Potential = U/q where q is the
“probe” or “sample charge.
Electric Potential is also known as Voltage =
V
The electric potential depends only on the
sources charge(s) and their geometry much
like Electric Field only depends on the source
charge.
U = qV (commonly used equation for finding
potential energy if you know the Voltage or
electric Potential)
Electric Potential
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For a Point Source, V = kq/r
Between 2 parallel plates with a uniform
electric field E, V = U/q = Ed
I remember this as Voltage = Ed for
parallel plates like a capacitor