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PHYS2114
LECTURE 7
Instructor: Professor Donna Bandy
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Capacitance
Defn Capacitor: Any two conductors separated by an
insulator (such as air) with charges equal in
magnitude and opposite in signs on the two plates.
parallel plates
1
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PHYS2114
LECTURE 7
Instructor: Professor Donna Bandy
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2
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PHYS2114
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3
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PHYS2114
LECTURE 7
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Parallel capacitors:
Series capacitors:
4
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PHYS2114
LECTURE 7
Instructor: Professor Donna Bandy
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Problem: For the system of four capacitors shown in Fig. 1 calculate the equivalent capacitance
of the system, the charge on each capacitor, and the potential difference across each capacitor.
Figure 1
5
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PHYS2114
ORANGE COUNTRY
GO COWBOYS
LECTURE 7
Instructor: Professor Donna Bandy
Capacitors (parallel plate) with Dielectrics






Air
Working voltage is the maximum potential difference where there is risk of “material
breakdown.”
Practical Capacitors
Dielectric Material
Dielectric constant   1
Breakdown Field (MV/m)
Air
1
3
Al
8.4
670
Glass (Pyrex)
5.6
14









Water
80
Conditiona
6
ORANGE COUNTRY
GO COWBOYS
PHYS2114
LECTURE 7
Instructor: Professor Donna Bandy
ORANGE COUNTRY
GO COWBOYS
Problem: Determine the capacitance and the maximum potential difference that can be applied
to a Teflon-filled parallel-plate capacitor having a plate area of 1.75 cm2 and a plate separation
of 0.04 mm.
7