Transcript Today`s Powerpoint

Chapter 21
Electric Potential
Topics:
• Electric potential energy
• Electric potential
• Conservation of energy
Sample question:
Shown is the electric potential measured on the surface of a patient.
This potential is caused by electrical 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?
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Slide 21-1
Checking Understanding
Rank in order, from largest to smallest, the electric
potentials at the numbered points.
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Slide 21-14
Example Problem
For the situation shown in the figure, find
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 105 m/s.
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 105 m/s.
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Slide 21-22
E-field lines and Equipotential lines
E-field Lines
• Go from + charges to - charges
• Perpendicular at surface of conductor or charged surface
• E-field in stronger where E-field lines are closer together
• More charge means more lines
Equipotential Lines
• Parallel to conducting surface
• Perpendicular to E-field lines
• Near a charged object, that charges influence is greater, then blends as
you to from one to the other
• E-field is stronger where Equipotential lines are closer together
• Spacing represents intervals of constant V
• Higher potential as you approach a positive charge; lower potential as you
approach a negative charge
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Slide 21-16
A Topographic Map
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Slide 21-12
Topographic Maps
1. Describe the region
represented by this map.
2. Describe the directions a
ball would roll if placed at
positions A – D.
3. If a ball were placed
at location D and
another ball were placed
at location C and both were
released,
which would have the greater acceleration?
Which has the greater potential energy when released?
Which will have a greater speed when at the bottom of the hill?
4. What factors does the speed at the bottom of the hill depend on? What factors
does the acceleration of the ball depend on?
5. Is it possible to have a zero acceleration, but a non-zero height? Is it possible
to have a zero height, but a non-zero acceleration?
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Slide 21-16
Equipotential Maps (Contour Maps)
1.Describe the charges that could
create equipotential lines such as
those shown above.
2.
2.Describe the forces a proton
would feel at locations A and B.
3. Describe the forces an electron
would feel at locations A and B
4.Where could an electron be
placed so that it would not move
5.At which point is the magnitude of the electric field the greatest?
5.
6. Is it possible to have a zero electric field, but a non-zero electric potential?
7. Is it possible to have a zero electric potential, but a non-zero electric field?
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Slide 21-16
3D view
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Slide 21-16
Connecting Potential and Field
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Slide 21-31
Reading Quiz
4. The electric field
A.
B.
C.
D.
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.
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Slide 21-12
Answer
4. The electric field
A.
B.
C.
D.
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.
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Slide 21-13
Example Problem
Source charges create the electric
potential shown.
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
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?
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Slide 21-33
Graphical Representations of Electric Potential
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Slide 21-13
The Potential Inside a Parallel-Plate Capacitor
Uelec
Q
V=
= Ex =
x
q
Î0 A
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Slide 21-25
Electric Potential of a Point Charge
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Slide 21-27