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Capacitance and
Dielectrics
• Chapter 26
All sections except 6
26.1
Definition of Capacitance
26.2
Calculating Capacitance
26.3 Combinations of Capacitors
26.4
Energy Stored in a Charged Capacitor
26.5
Capacitors with Dielectrics
26.7
An Atomic Description of Dielectrics
PHYS142 Lecture 10
2
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View Full Document Definition of Capacitor (26.1)
A pair of conducting objects (surfaces) separated by a gap
constitute a
capacitor
.
If a
capacitor
is connected to a
battery
, after a very short
time each plate acquires a charge.
+
+
+
+
+
+
_
_
_
_
_
_
V
+
Q

Q
+
–
6
The amount of charge is directly proportional to the potential
difference of the battery.
Q ~ V
The charge on the capacitor is defined to be the charge on its
positively charged plate
.
Q = CV
Where
C
is the
capacitance
of the capacitor.
Capacitance refers to the “capacity to accumulate charges”
If
C
is large, so is
Q
for a given
V
.
Units for Capacitance:
C/V
Farad [F]
Definition of capacitance
7
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View Full Document True or False? From the definition of capacitance C = Q/ΔV,
it follows that an
uncharged capacitor
has a
capacitance of
zero
.
1
2
72%
28%
1.
True
2.
False
Question 1
True or False? (a) As described by the definition of
capacitance C = Q/ΔV, it follows that the
potential
difference
across an
uncharged
capacitor is zero.
1
2
23%
77%
1.
True
2.
False
Question 2
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View Full Document The capacitance
C
depends on the construction of the
capacitor i.e. its geometry and the material in the gap.
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This note was uploaded on 02/22/2011 for the course PHYS 142 taught by Professor Altounian during the Spring '07 term at McGill.
 Spring '07
 ALTOUNIAN
 Capacitance, Charge, Magnetism, Energy

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