FOR SCIENTISTS AND ENGINEERS
A STRATEGIC APPROACH
4/E
PHYSICS
RANDALL D. KNIGHT
Chapter 25 Lecture
Slide 25-1
Chapter 25 The Electric Potential
IN THIS CHAPTER, you will learn to use the electric potential and electric potential energy.
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Chapter 25 Preview
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Chapter 25 Preview
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Chapter 25 Preview
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Chapter 25 Preview
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Chapter 25 Preview
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Chapter 25 Preview
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Chapter 25 Reading Questions
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The electric potential energy of a system of two point charges is proportional to
Reading Question 25.1
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The electric potential energy of a system of two point charges is proportional to
Reading Question 25.1
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What are the units of potential difference?
Reading Question 25.2
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What are the units of potential difference?
Reading Question 25.2
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New units of the electric field were introduced in this chapter. They are
Reading Question 25.3
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New units of the electric field were introduced in this chapter. They are
Reading Question 25.3
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Which of the following statements about equipotential surfaces is true?
Reading Question 25.4
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Which of the following statements about equipotential surfaces is true?
Reading Question 25.4
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The electric potential inside a capacitor
Reading Question 25.5
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The electric potential inside a capacitor
Reading Question 25.5
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Chapter 25 Content, Examples, and QuickCheck Questions
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Energy
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Work Done by a Constant Force
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A Gravitational Analogy
Wgrav = mgyi – mgyf
ΔUgrav = – Wgrav
where
Ugrav = U0 + mgy
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Two rocks have equal mass. Which has more gravitational potential energy?
QuickCheck 25.1
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Two rocks have equal mass. Which has more gravitational potential energy?
QuickCheck 25.1
Increasing PE
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A Uniform Electric Field
Welec = qEsi – qEsf
ΔUelec = –Welec
where
Uelec = U0 + qEs
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Two positive charges are equal. Which has more electric potential energy?
QuickCheck 25.2
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Two positive charges are equal. Which has more electric potential energy?
QuickCheck 25.2
Increasing PE
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Electric Potential Energy in a Uniform Field
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Electric Potential Energy in a Uniform Field
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Electric Potential Energy in a Uniform Field
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Electric Potential Energy in a Uniform Field
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Two negative charges are equal. Which has more electric potential energy?
QuickCheck 25.3
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Two negative charges are equal. Which has more electric potential energy?
QuickCheck 25.3
Increasing PE for negative charge
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A positive charge moves as shown. Its kinetic energy
QuickCheck 25.4
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A positive charge moves as shown. Its kinetic energy
QuickCheck 25.4
Increasing PE
Decreasing KE
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The Potential Energy of Two Point Charges
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The Potential Energy of Point Charges
The Potential Energy of Two Point Charges
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The Potential Energy of Two Point Charges
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The Potential Energy of Two Point Charges
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A positive and a negative charge are released from rest in vacuum. They move toward each other. As they do,
QuickCheck 25.5
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A positive and a negative charge are released from rest in vacuum. They move toward each other. As they do,
QuickCheck 25.5
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The Electric Force Is a Conservative Force
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Example 25.2 Approaching a Charged Sphere
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Example 25.2 Approaching a Charged Sphere
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Example 25.2 Approaching a Charged Sphere
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Example 25.3 Escape Speed
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Example 25.3 Escape Speed
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Example 25.3 Escape Speed
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Example 25.3 Escape Speed
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The Potential Energy of Multiple Point Charges
where rij is the distance between qi and qj.
The Potential Energy of Multiple Point Charges
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Example 25.4 Launching an Electron
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Example 25.4 Launching an Electron
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Example 25.4 Launching an Electron
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Example 25.4 Launching an Electron
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The Potential Energy of a Dipole
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The Potential Energy of a Dipole
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Example 25.5 Rotating a Molecule
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Example 25.5 Rotating a Molecule
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The Electric Potential
This battery is a source of electric potential. The electric potential difference between the + and – sides is 1.5 V.
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The Electric Potential
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Using the Electric Potential
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A proton is released from rest at the dot. Afterward, the proton
QuickCheck 25.6
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A proton is released from rest at the dot. Afterward, the proton
QuickCheck 25.6
Decreasing PE
Increasing KE
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If a positive charge is released from rest, it moves in the direction of
QuickCheck 25.7
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If a positive charge is released from rest, it moves in the direction of
QuickCheck 25.7
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Problem-Solving Strategy: Conservation of Energy in Charge Interactions
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Problem-Solving Strategy: Conservation of Energy in Charge Interactions
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Example 25.6 Moving Through a Potential Difference
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Example 25.6 Moving Through a Potential Difference
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Example 25.6 Moving Through a Potential Difference
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Example 25.6 Moving Through a Potential Difference
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Example 25.6 Moving Through a Potential Difference
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The Electric Field Inside a Parallel-Plate Capacitor
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The Electric Potential Inside a Parallel-Plate Capacitor
where s is the distance from the negative electrode.
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Units of Electric Field
1 N/C = 1 V/m
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The Electric Potential Inside a Parallel-Plate Capacitor
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The Electric Potential Inside a Parallel-Plate Capacitor
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Two protons, one after the other, are launched from point 1 with the same speed. They follow the two trajectories shown. The protons’ speeds at points 2 and 3 are related by
QuickCheck 25.8
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Two protons, one after the other, are launched from point 1 with the same speed. They follow the two trajectories shown. The protons’ speeds at points 2 and 3 are related by
QuickCheck 25.8
Energy conservation
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The Parallel-Plate Capacitor
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The Zero Point of Electric Potential
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The Electric Potential of a Point Charge
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The Electric Potential of a Point Charge
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What is the ratio VB/VA of the electric potentials at the two points?
QuickCheck 25.9
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What is the ratio VB/VA of the electric potentials at the two points?
QuickCheck 25.9
Potential of a point charge decreases inversely with distance.
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The Electric Potential of a Point Charge
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The Electric Potential of a Point Charge
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The Electric Potential of a Charged Sphere
where r ≥ R.
A plasma ball consists of a small metal ball inside a hollow glass sphere filled with low-pressure neon gas. The high voltage of the ball creates “lightning bolts” between the ball and the glass sphere.
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An electron follows the trajectory shown from i to f. At point f,
QuickCheck 25.10
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An electron follows the trajectory shown from i to f. At point f,
QuickCheck 25.10
Increasing PE (becoming less negative) so decreasing KE
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Example 25.8 A Proton and a Charged Sphere
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Example 25.8 A Proton and a Charged Sphere
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Example 25.8 A Proton and a Charged Sphere
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Example 25.8 A Proton and a Charged Sphere
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where ri is the distance from charge qi to the point in space where the potential is being calculated.
The Electric Potential of Many Charges
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The Electric Potential of an Electric Dipole
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The Electric Potential of a Human Heart
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At the midpoint between these two equal but opposite charges,
QuickCheck 25.11
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At the midpoint between these two equal but opposite charges,
QuickCheck 25.11
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At which point or points is the electric potential zero?
QuickCheck 25.12
A.
B.
C.
D.
E. More than one of these.
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At which point or points is the electric potential zero?
QuickCheck 25.12
A.
B.
C.
D.
E. More than one of these.
V = 0
V = 0
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Example 25.9 The Potential of Two Charges
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Example 25.9 The Potential of Two Charges
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Example 25.9 The Potential of Two Charges
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Problem-Solving Strategy: The Electric Potential of a Continuous Distribution of Charge
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Problem-Solving Strategy: The Electric Potential of a Continuous Distribution of Charge
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Example 25.10 The Potential of a Ring of Charge
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Example 25.10 The Potential of a Ring of Charge
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Example 25.10 The Potential of a Ring of Charge
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Example 25.10 The Potential of a Ring of Charge
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Example 25.10 The Potential of a Ring of Charge
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Chapter 25 Summary Slides
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General Principles
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General Principles
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Applications
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Applications
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