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Chapter 25:
Capacitors
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For a “charged” capacitor, one
conductor is +
the other is –
(net charge is zero)
•
The work used in separating
charge is stored as electrostatic
potential energy in the capacitor.
C
apacitor:
A pair of conductors,
insulated from each other,
used to store energy
Definition of Capacitance C
q
C
V
+q
q
V
Charge q is proportional to potential
difference V between the plates
Units: farad [F]
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View Full Document ParallelPlate capacitor
What is the capacitance of a
parallel plate capacitor of area
A
and separation
d
?
(Work out on board)
0
A
C
d
Depends on geometry!
Fringe field
outside
5
L
L
d
A parallelplate capacitor has square plates of edge length L,
separated by a distance d.
If we doubled the dimension L and halve the dimension d,
by what factor have we changed the capacitance?
A)1.0
B) 2.0
C) 4.0
D) 16.0
E) None of the above.
0
A
C
d
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How big is a one Farad Capacitor?
Assume you have two parallel plates that are separated by 1 mm.
If you estimate
0
~ 10
11
, what is the area of the plates to have a
1.0 Farad capacitance?
A)100,000,000 square meters
B) 1,000 square meters
C)
1 square meter
D)
0.1 square meters
E)
0.001 square meters
0
A
C
d
7
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This note was uploaded on 02/05/2011 for the course PHYS 220B taught by Professor Preminger during the Fall '10 term at CSU Northridge.
 Fall '10
 Preminger
 Charge, Energy, Work

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