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Chapter 21 Reading Quiz Electric Potentialphysics.gsu.edu/dhamala/Phys1112/Slides/Chapter21.pdf ·...
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• Electric potential energy • Electric potential • Conservation of energy • Potential and field • Capacitors and capacitance Chapter 21 Electric Potential Topics: Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. • Capacitors and capacitance Sample question: Shown is the electric potential me This potential is caused by electri heart. Why does the potential hav measurements tell us about the h easured on the surface of a patient. ical signals originating in the beating ve this pattern, and what do these heart’s condition? Slide 21-1 Reading Quiz 1. What are the units of potential Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. difference? Slide 21-2 Reading Quiz 2. New units of the electric field w chapter. They are: A. V/C B. N/C C. V/m D. J/m 2 E. Ω/m Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. F. J/C were introduced in this Slide 21-3 2. New units of the electric field w chapter. They are: C. V/m Answer Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. were introduced in this Slide 21-4
Transcript of Chapter 21 Reading Quiz Electric Potentialphysics.gsu.edu/dhamala/Phys1112/Slides/Chapter21.pdf ·...
• Electric potential energy
• Electric potential
• Conservation of energy
• Potential and field
• Capacitors and capacitance
Chapter 21
Electric Potential
Topics:
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
• Capacitors and capacitance
Sample question:
Shown is the electric potential me
This potential is caused by electricheart. Why does the potential have this pattern, and what do these measurements tell us about the heart’s condition?
easured on the surface of a patient.
trical signals originating in the beating heart. Why does the potential have this pattern, and what do these measurements tell us about the heart’s condition?
Slide 21-1
Reading Quiz
1. What are the units of potential difference?
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What are the units of potential difference?
Slide 21-2
Reading Quiz
2. New units of the electric field were introduced in this
chapter. They are:
A. V/C
B. N/C
C. V/m
D. J/m2
E. Ω/m
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E. Ω/m
F. J/C
2. New units of the electric field were introduced in this
Slide 21-3
2. New units of the electric field were introduced in this
chapter. They are:
C. V/m
Answer
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2. New units of the electric field were introduced in this
Slide 21-4
Reading Quiz
3. The electric potential inside a parallel
A. is constant.
B. increases linearly from the negative to the positive plate.
C. decreases linearly from the negative to the positive plate.
D. decreases inversely with distance from the negative plate.
E. decreases inversely with the square of the distance from
the negative plate.
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the negative plate.
The electric potential inside a parallel-plate capacitor
increases linearly from the negative to the positive plate.
decreases linearly from the negative to the positive plate.
decreases inversely with distance from the negative plate.
decreases inversely with the square of the distance from
Slide 21-5
3. The electric potential inside a parallel
B. increases linearly from the negative to the positive plate.
Answer
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The electric potential inside a parallel-plate capacitor
increases linearly from the negative to the positive plate.
Slide 21-6
Reading Quiz
4. The electric field
A. is always perpendicular to an equipotential surface.
B. is always tangent to an equipotential surface.
C. always bisects an equipotential surface.
D. makes an angle to an equipotential surface that depends
on the amount of charge.
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is always perpendicular to an equipotential surface.
is always tangent to an equipotential surface.
always bisects an equipotential surface.
makes an angle to an equipotential surface that depends
on the amount of charge.
Slide 21-7
4. The electric field
A. is always perpendicular to an equipotential surface.
Answer
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is always perpendicular to an equipotential surface.
Slide 21-8
Electric Potential Energy
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Potential Energy
BABAAB mghmghW GPEGPE −=−=
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B
10
Potential Energy
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11
Potential Energy
BAABW EPEEPE −=
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12
The Electric Potential Difference
o
B
o
A
o
AB
qqq
W EPEEPE−=
The potential energy per unit charge
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The potential energy per unit chargeis called the electric potential.The potential energy per unit charge
13
The potential energy per unit charge
The Electric Potential Difference
DEFINITION OF ELECTRIC POTENTIAL
The electric potential at a given point is the electric potential energy of a small test charge divided by the charge itself:
oqV
EPE=
SI Unit of Electric Potential: joule/coulomb = volt (V)
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SI Unit of Electric Potential: joule/coulomb = volt (V)
o
BAB
qVV −=−
EPEEPE
( )
oqV
∆=∆
EPE
DEFINITION OF ELECTRIC POTENTIAL
The electric potential at a given point is the electric potential energy of a small test charge divided by the charge itself:
EPE
joule/coulomb = volt (V)
14
joule/coulomb = volt (V)
o
AB
o
A
q
W
q
−=
EPE
)
o
AB
q
W−=
Electric Potential
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Uelec
= qV; VV = Uelec
/ q
Slide 21-10
Exercise
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Is the change ∆U of the particle positive, negative, or
zero as it moves from i to f?
of the particle positive, negative, or
zero as it moves from i to f?
Slide 21-11
A Topographic Map
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Graphical Representations of Electric Potential
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Graphical Representations of Electric Potential
Slide 21-13
Checking Understanding
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Rank in order, from largest to smallest, the electric
potentials at the numbered points.
Rank in order, from largest to smallest, the electric
potentials at the numbered points.
Slide 21-14 Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 21-15
Example
A proton has a speed of 3.5 x 105
electrical potential is 600 V. It moves through a point where the electric potential is 1000 V. What is its speed at this second point?
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5 m/s at a point where the electrical potential is 600 V. It moves through a point where the electric potential is 1000 V. What is its speed at this second point?
Slide 21-16
Example
A proton is released from rest at pWhat is its speed at point b?
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t point a. It then travels past point b.
Slide 21-17
The Potential Inside a Parallel
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V = Ex =Q
ε0
The Potential Inside a Parallel-Plate Capacitor
Q
0A
x =∆V
C
dx
Slide 21-18
Example
A parallel-plate capacitor is held at a potential difference of 250 V.
A proton is fired toward a small hole in the negative plate with a speed of 3.0 x 105 m/s. What is its speed when it emerges through the hole in the positive plate? (Hint: The electric potential outside of a parallel-plate capacitor is zero).
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plate capacitor is held at a potential difference of 250 V.
A proton is fired toward a small hole in the negative plate with a m/s. What is its speed when it emerges through
the hole in the positive plate? (Hint: The electric potential outside plate capacitor is zero).
Slide 21-19
Electric Potential of a Point Charge
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V = Kq
r=
4
Electric Potential of a Point Charge
1
4πε0
q
r
Slide 21-20
Electric Potential: Charged Sphere
Outside of a sphere of charge Q thfor a point charge Q:
V =1
4π
If the sphere has radius R and the potential at its surface is
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If the sphere has radius R and the potential at its surface is the potential a distance r from its center can also be written
V =R
r
Electric Potential: Charged Sphere
the potential has the same form as
1
πε0
Q
r
and the potential at its surface is V0, then and the potential at its surface is V0, then from its center can also be written
RV
0
Slide 21-21
Example
For the situation shown in the figure, find
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A. The potential at points a and b.The potential difference between a and b.
B. The potential energy of a proton at a and b.
C. The speed at point b of a proton that was moving to the right at point a with a speed of 4.0 x 10
D. The speed at point a of a proton that was moving to the left at point b with a speed of 4.0 x 10
For the situation shown in the figure, find
The potential at points a and b.The potential difference between
The potential energy of a proton at a and b.
The speed at point b of a proton that was moving to the right at 105 m/s.
The speed at point a of a proton that was moving to the left at 105 m/s.
Slide 21-22
Example
A 2.0-mm-diameter plastic bead is charged to
A. A proton is fired at the bead from far away with a speed of
1.0 x 106 m/s, and it collides headspeed?
B. An electron is fired at the bead from far away. It “reflects,” with a turning point 0.10 mm from the surface of the bead.
What was the electron’s initial speed?
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diameter plastic bead is charged to –1.0 nC.
A proton is fired at the bead from far away with a speed of
m/s, and it collides head-on. What is the impact
An electron is fired at the bead from far away. It “reflects,” with a turning point 0.10 mm from the surface of the bead.
What was the electron’s initial speed?
Slide 21-23
Connecting Potential and Field
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Connecting Potential and Field
Slide 21-24
Potential and Field for Three Important Cases
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Potential and Field for Three Important Cases
Slide 21-25
A. What is the potential at point A? At which point, A, B, or C,
does the electric field have its largest magnitude?
B. Is the magnitude of the electric
field at A greater than, equal
Example
Source charges create the electric
potential shown.
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field at A greater than, equal to, or less than at point D?
C. What is the approximate magnitude of the electric field at
point C?
D. What is the approximate direction of the electric field at
point C?
A? At which point, A, B, or C,
does the electric field have its
Is the magnitude of the electric
Source charges create the electric
What is the approximate magnitude of the electric field at
What is the approximate direction of the electric field at
Slide 21-26
A Conductor in Electrostatic Equilibrium
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A Conductor in Electrostatic Equilibrium
Slide 21-27
Exercise
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What is Q2??
Slide 21-28
Capacitance and Capacitors
The charge
is proportional to the potential difference electrodes:
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Capacitance and Capacitors
Q = C∆V
The charge ±Q on each electrode
is proportional to the potential difference ∆VC between the electrodes:
Q = C∆VC
Slide 21-29
Charging a Capacitor
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The Capacitance of a Parallel
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The Capacitance of a Parallel-Plate Capacitor
C =ε
0A
dd
Slide 21-31
Dielectrics and Capacitors
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Dielectric Constant
With a dielectric between its plates, the capacitance of a parallel-plate capacitor is increased by a factor of the dielectric constant κ:
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C =κε
0A
d
Slide 21-33
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