Today 3/10

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Today 3/10

• Plates if charge
• E-Field
• Potential
• HW Plates of Charge Due Thursday, 3/13
• Lab Electric Deflection of Electrons

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Looking from farther away
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We call this an infinite plate.
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Field lines for a positive plate
? is the charge on each square meter of the
plate.
Near the plate the field lines must (by symmetry)
point directly away from the plate.
?()
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Field lines for a plate
?()
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Field lines for a negative plate
Cant tell if the field is caused by a pos plate
below or a neg plate above!
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Size of the E-field
For plates
?0 8.8x10-12 C2/Nm2
Note no dependence on distance
For point charges
k 9.0x109 Nm2/C2
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Two Parallel Plates
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Two Parallel Plates
?()
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Two Parallel Plates
Enet
?()
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Two Parallel Plates
Enet
Enet
?()
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Two Parallel Plates
Enet
Enet
?()
Enet 0
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How big is E?
Enet
?()
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How big is E?
?()
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What do the field lines look like?
?()
E 0 outside!
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Points A and B are located as shown between two
large uniformly charged parallel plates. Which
of the following correctly describes what happens
to the electric fields at A and B if the plate on
the right is removed?
a. The field at A drops more than the field at
B. b. The field at B drops more than the field at
A. c. The fields at A and B remain that same. d.
The fields at A and B drop by the same amount.
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Charged conducting plate
A Area of one side
?0 Q/A
Whats wrong with this picture?
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Charged conducting plate
?L ?0/2
?R ?0/2
Free charge always goes to surface of conductor.
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Charged conducting plate
?L ?0/2
?R ?0/2
EL ?L/2e0
EL ?0/4e0
What is the electric field inside the conductor?
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Charged conducting plate
?L ?0/2
?R ?0/2
What is the electric field inside the conductor?
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Charged conducting plate
?L ?0/2
?R ?0/2
The electric field is zero everywhere inside the
conductor.
What is the electric field inside the conductor?