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EEEB113
CIRCUIT ANALYSIS I
Chapter 6
Capacitors and Inductors
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Materials from Fundamentals of Electric Circuits, Alexander & Sadiku 4e, McGraw-Hill.
Capacitors and Inductors Chapter 6
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6.1 Capacitors
6.2 Series and Parallel Capacitors
6.3 Inductors
6.4 Series and Parallel Inductors

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6.1 Capacitors (1)
 A capacitor is a passive element designed to
store energy in its electric field.
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• A capacitor consists of two conducting plates
separated by an insulator (or dielectric).
6.1 Capacitors (2)
 Capacitance C is the ratio of the charge q on one
plate of a capacitor to the voltage difference v
between the two plates, measured in farads (F).
4
• Where is the permittivity of the dielectric material
between the plates, A is the surface area of each
plate, d is the distance between the plates.
• Unit: F, pF (10–12), nF (10–9), and
vCq
d
A
Cand
F (10–6)

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6.1 Capacitors (3)
 If i is flowing into the +ve
terminal of C
 Charging => i is +ve
 Discharging => i is –ve
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• The current-voltage relationship of capacitor
according to above convention is
td
vd
Ci )(
1
0
0
tvtdi
C
v
t
t
and
6.1 Capacitors (4)
 The energy, w, stored in
the capacitor is
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• A capacitor is
– an open circuit to dc (dv/dt = 0).
– its voltage cannot change abruptly.
2
2
1
vCw

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6.2 Series & Parallel Capacitors (1)
 The equivalent capacitance of N parallel-
connected capacitors is the sum of the individual
capacitances.
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Neq CCCC ...21
6.2 Series & Parallel Capacitors (2)
 The equivalent capacitance of N series-connected
capacitors is the reciprocal of the sum of the
reciprocals of the individual capacitances.
8
Neq CCCC
1
...
111
21

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6.3 Inductors (1)
 An inductor is a passive element designed
to store energy in its magnetic field.
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• An inductor consists of a coil of conducting wire.
6.3 Inductors (2)
 Inductance is the property whereby an inductor
exhibits opposition to the change of current
flowing through it, measured in henrys (H).
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• The unit of inductors is Henry (H), mH (10–3)
and H (10–6).
td
id
Lv
l
AN
L
2
and

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6.3 Inductors (3)
 The current-voltage relationship of an inductor:
11
• The power stored by an inductor:
)()(
1
0
0
titdtv
L
i
t
t
2
2
1
iLw
• An inductor acts like a short circuit to dc (di/dt = 0)
and its current cannot change abruptly.
6.4 Series & Parallel Inductors (1)
 The equivalent inductance of series-connected
inductors is the sum of the individual
inductances.
12
Neq LLLL ...21

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6.4 Series & Parallel Inductors (2)
 The equivalent capacitance of parallel inductors is the
reciprocal of the sum of the reciprocals of the
individual inductances.
13
Neq LLLL
1
...
111
21
Summary
 Current and voltage relationship for R, L, C
14
+
+
+

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