Transcript Electric Potential Difference

5.4 Electric energy, Electric Potential, and
Electric Potential Difference
Electric Potential Energy In Uniform Fields
The Work-Energy theorem states that work done on an object is equal to the
change in object’s energy.
W = ΔEp
This equation applies to all types of
energy including gravitational potential
energy and electric potential energy. In
both cases lines of force show the
direction that either a massive object or a
charged object would move do to the
gravitational or electric field.
p. 187 - 188
5.4 Electric energy, Electric Potential, and
Electric Potential Difference
Electric Field, Energy and Charges:
The positive charge would gain electric potential
energy as it moves from position A to position B.
Of course a negative charge would gain electric
potential energy as it moved form position B to
position A.
When a positive charge spontaneously moves from
position B to position A, it loses electric potential energy
and gain kinetic energy (it will increase its speed) very
much like a falling object.
p. 189
5.4 Electric energy, Electric Potential, and
Electric Potential Difference
Electric Potential Energy of Multiple Charges – Non-Uniform Field
Potential energy must be specified to a reference location. For electric potential energy we
use distance set to infinity to set electric potential energy to zero at this point
W = Fe x d
And since :
Fe =
W = Ep =
Ep =
k Q1Q2
r2
k Q1Q2
xd
(and d = r)
r2
k Q1Q2
r
p. 190 - 192
5.4 Electric energy, Electric Potential, and
Electric Potential Difference
Electric Potential Energy of Multiple Charges – Non-Uniform Field
Determining the work done in moving a charge is accomplished by calculating the change in
potential energy. For example :A charge Q1 is moved form d1 to d2 relative to charge Q2.
d1
d2
Q1
Q2
To calculate the work done:
W = ΔEp =
k Q1Q2
d2
-
k Q1Q2
d1
p. 192
5.4 Electric energy, Electric Potential, and
Electric Potential Difference
Electric Potential – It’s all about location
Electric potential is defined as the amount of work (energy) required to move a unit charge
to a point in an electric field.
ΔEp
V =
Q
Units: 1 Volt = 1 Joule/coulomb
Electric potential is used to express the effect of a source’s electric field in terms of
location within the electric field.
Electric potential is a property of the location of a charge within an electric
field, and not of the amount of charge.
p. 193
5.4 Electric energy, Electric Potential, and
Electric Potential Difference
Electric Potential of Single Point Charges
To calculate the electric potential at some distance from a point charge:
ΔEp
V =
=
Q
k Q1Q2
P
Qr
r
Cancelling out one of the charges leave you with:
V =
kQ
r
Q
p. 194
5.4 Electric energy, Electric Potential, and
Electric Potential Difference
Electric Potential Difference
To calculate the electric potential difference or Voltage as a charge moves in an electric field:
VAB =
ΔEpB
ΔEpA
Q
Q
WAB
VAB =
Q
(WAB = ΔEpB – ΔEpA)
The potential difference (V) between two points is defined as the amount of work
required to move a unit of positive charge from the point that is lower potential to the
point that is at the higher potential.
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5.4 Electric energy, Electric Potential, and
Electric Potential Difference
Electron Volt
On the atomic scale the Joule is a very large amount of energy. A smaller unit of
energy, the electron volt (eV) is used.
-
+
1 eV is the energy gained when 1 electron is
accelerated by a potential difference of 1 volt.
electron
1 eV = 1.6 x 10-19 J
p. 196
5.4 Electric energy, Electric Potential, and Electric Potential Difference
Key Questions
In this section, you should understand how to solve the following key questions.
Page 189 – Quick Check #2
Page 191 – Practice Problem 5.4.1: #1 & 2
Page 195 – Quick Check #2
Page 196 – Practice Problem 5.4.2: #3
Page 197 – Practice Problem 5.4.3: #2
Page 198 - 199 – Review 5.4 #2,4,6,8, 12 & 13