Physics with Calculus II

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Physics with Calculus II
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(No Transcript)
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Where weve been

• Mechanics
• The Electric Field
• Gausss Law

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Ch 25 Introduction
The electrostatic force is a conservative force
and, therefore, it is meaningful to talk about an
electric potential energy. This in turn enables
us to define an electrostatic potential, a
concept simpler than force to understand, because
it is a scalar, in describing circuits and many
other electrical phenomena.
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Where were going
Ch 25 Electric Potential (25.1) Potential
Difference and Electric Potential (25.2)
Potential Differences in uniform E (25.3)
Electric Potential Potential Energy (25.4)
Obtain E from Electric Potential (25.5) When
charge is not point charge (25.7) Millikan
measuring charge of electron
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(25.1) Potential Difference and Electric Potential
Change in Potential Energy
Which decreases U of Electric Field by
More
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(25.1) Potential Difference and Electric
Potential, contd
For finite displacement of test charge between A,
B
Path NOT important !
More
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(25.1) Potential Difference and Electric
Potential, contd
Page 769 The Potential Energy per unit charge (
U / q0 ) is INdependent of the value of q 0 and
has a unique value at EVERY point in the Electric
Field.
A scalar !
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(25.1) Potential Difference and Electric
Potential, contd
Potential Difference ?
Potential Difference ? Potential Energy
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(25.1) Potential Difference and Electric
Potential, contd
The Electric Potential (V) _at_ some arbitrary point
(P) equals the work per charge done to bring a
test charge from infinity to that point.
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(25.1) Potential Difference and Electric
Potential, contd
Some more units A unit of energy
Another unit for Electric Field (E)
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(25.1) Potential Difference and Electric
Potential, contd
A problem not in your text A spark plug in your
gasoline engine Gap 0.060 cm E 3.0 (106)
V/m Calculate ? V of the gap
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(25.2) Potential Differences in uniform E
Again, work done in moving q from A to B is
INDEPENDENT of path taken.
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(25.2) Potential Differences in uniform E, contd
Equipotential Surface Any surface consisting of
a continuous distribution of points having the
same Electric Potential (V).
Equipotential Line Any line consisting of a
continuous distribution of points having the same
Electric Potential (V).
Problem 25.6
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(25.3) Electric Potential Potential Energy
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(25.3) Electric Potential Potential Energy,
contd
From Previous Slide
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(25.3) Electric Potential Potential Energy,
contd
ONLY for point charges !
Problem 25.20
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(25.4) Obtain E from Electric Potential
From Earlier
Now, if we only evaluate one component (one axis)
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(25.4) Obtain E from Electric Potential, contd
And,
Problem 25.37
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(25.5) V due to continuous charge distribution
Aka V when charge is not a point charge
And, of course
Problem 25.43
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• The End