Fundamentals of Electric Circuits
(EE201)
Chap 6: Capacitors and
Inductors
By
Dr. Eng. Omar Abdel-Gaber M. Aly
omar.aly@aun.edu.eg
Assistant Professor
Electrical Engineering Department
College of Engineering Al-Majmaa
Al-Majmaa University
CAPACITORS


The capacitance c = q/v F
The current-voltage relationship of the capacitor:
t
t
1
1
dq
dv
v   idt   idt  v(to )
i
c
c 
c to
dt
dt
where v(t0)=q(t0)/C is the voltage across the capacitor at time t0.
 The instantaneous power p and energy w:
p  vi  cv
dv
dt
1 2 q2
w  cv 
2
2c

An ideal capacitor cannot dissipate energy instead its store
energy in an electric field.
Fundamentals of Electric Circuits, by Dr.
Omar Aly
2
CAPACITORS

1.
2.
3.
We should note the following important properties of a
capacitor:
A capacitor is an open circuit to dc.
The voltage on a capacitor cannot change abruptly. A discontinuous change in voltage requires an infinite current, which is
physically impossible.
The ideal capacitor does not dissipate energy. It takes power
from the circuit when storing energy in its field and returns
previously stored energy when delivering power to the circuit.
Fundamentals of Electric Circuits, by Dr.
Omar Aly
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Example 6.2
The voltage across a 5-μF capacitor is v(t)= 10 cos 6000t V
Calculate the current through it.
Solution:
By definition, the current is

Fundamentals of Electric Circuits, by Dr.
Omar Aly
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Example 6.4

Determine the current through a 200-μF capacitor whose
voltage is shown in Fig.
Fundamentals of Electric Circuits, by Dr.
Omar Aly
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EXAMPLE 6.5
Obtain the energy stored in each capacitor in Fig under dc
conditions.
Solution:
Under dc conditions, we replace each capacitor
with an open circuit.

Fundamentals of Electric Circuits, by Dr.
Omar Aly
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INDUCTORS
An inductor is a passive element designed to store energy
in its magnetic field. They are used in power supplies,
transformers, radios, TVs, radars, and electric motors.
 the voltage across
the inductor is
L = inductance it’s unit is the henry (H),
The current-voltage relationship

The instantaneous power p and energy w:
Fundamentals of Electric Circuits, by Dr.
Omar Aly
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INDUCTORS

1.
2.
3.
We should note the following important properties of an
inductor.
An inductor acts like a short circuit to dc.
The current through an inductor cannot change
instantaneously.
Ideal inductor does not dissipate energy. The inductor
takes power from the circuit when storing energy and
delivers power to the circuit when returning previously
stored energy.
Fundamentals of Electric Circuits, by Dr.
Omar Aly
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Example 6.8

The current through a 0.1-H inductor is i(t) = 10te−5t A.
Find the voltage across the inductor and the energy stored
in it.
Fundamentals of Electric Circuits, by Dr.
Omar Aly
9
Example 6.10

Find the current through a 5-H inductor if the voltage
across it is

Also find the energy stored within 0 < t < 5 s.
Fundamentals of Electric Circuits, by Dr.
Omar Aly
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Example 6.10
Consider the circuit shown. Under dc
conditions, find: (a) i, vC, and iL, (b) the
energy stored in the capacitor and inductor.

Fundamentals of Electric Circuits, by Dr.
Omar Aly
11
SERIES AND PARALLEL
INDUCTORS
The equivalent inductance of series
-connected inductors is the sum of the
individual inductances.

The equivalent inductance of parallel
inductors is the reciprocal of the sum of
the reciprocals of the individual
inductances.

Fundamentals of Electric Circuits, by Dr.
Omar Aly
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Example 6.12

For the circuit in Fig, i(t) = 4(2 − e−10t ) mA. If i2(0)=−1mA,
find: (a) i1(0); (b) v(t), v1(t), and v2(t); (c) i1(t) and i2(t).
Fundamentals of Electric Circuits, by Dr.
Omar Aly
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Example 6.12
Fundamentals of Electric Circuits, by Dr.
Omar Aly
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Problems Chp6, Page 227
1, 2, 4, 5, 6, 8, 9, 12, 17, 29
 30, 31, 34, 35, 36, 38, 39, 40, 44, 53

Fundamentals of Electric Circuits, by Dr.
Omar Aly
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