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DET 101/3
Bacis Electrical Circuit 1
List of text book and references
Text book:
1. Charles K. Alexander & Matthew Sadiku, “Fundamental
of Electric Cicuit”, International Edition, McGraw
Hill,2001.
References:
1. J.David Irwin & Chwan-Hwa WU,”Basic Engineering
Circuit Analysis”,John Wiley & Son,7th edition,2001.
2. Nilsson,J.W. & Riedel, S.A,”Electric Circuit”,5th Edition,
Addison Wesley,1996.
3. J.David Irwin,”Basic Engineering Circuit
Analysis”,International Edition, 5th Edition, Prentice
Hall, 1996.
GRADING
THEORY ( 60%)
1. Final Exam 50%
2. Test 1 & 2 10%
 PRACTICAL ( 40%)
1. Laboratory (7 modules) 30%
2. Lab Test
10%
Variables & Cct Elements
International System of Units, SI
Current and Voltage
Power and Energy
Ideal Basic Circuit Elements
Basic Circuit Connections
Application of Passive Sign Convention
to Ohm’s Law and Power Calculation
Kirchhoff’s Laws
Introduction
There are several ways of describing or
defining electric circuit:
 Definition 1: Electric circuit is a mathematical
model that approximates the behavior of an
actual electrical system. Hence the analysis of a
circuit is a study of the behavior of the circuits.
 Definition 2: Electric circuit can be defined as an
interconnection between components or
electrical devices for the purpose of
communicating or transferring energy from one
point to another. The components of electric
circuit are always referred to as circuit elements.
International System of Units (SI)
Quantity
Basic Unit
Symbol
Length
Meter
m
Mass
Kilogram
kg
Time
Second
s
Electric current
Ampere
A
Thermodynamic
temperature
Kelvin
K
Luminous intensity
Candela
cd
International System of Units (SI)
Multiplier
Prefix
Symbol
1018
Exa
E
1015
Peta
P
1012
Tera
T
109
Giga
G
106
Mega
M
103
Kilo
k
102
Hector
h
101
Deka
da
10-1
Deci
d
10-2
Centi
d
10-3
Mili
m
10-6
Micro

10-9
Nano
n
10-12
Pico
p
10-15
Femto
f
10-18
Atto
a
Current and Voltage
I or V
I or V
t
0
t
0
(a)
(b)
Figure 1.1: Two common types of signals
(a) constant or direct current/voltage.
(b) time-varying or alternating
current/voltage.
Current and Voltage
The electric current is the rate of change
of charge over time, measured in
amperes, A. Mathematically, current i,
expressed in terms of charge, q and time, t
is:
i = dq/dt
in coulomb/second or amperes.
Current and Voltage
Voltage is defined as energy, w per unit
charge, q created by the separation.
Mathematically, we express this in
differential form as:
v = dw/dq
in Joules/coulomb or volts
Power and Energy
Reason why we should know about power
and energy.
 1st reason: Practically, any electrical devices have
limitation in the power rating that they can handle.
Exceeding the prescribed rating could destroy or make
the device to malfunction.
 2nd reason: We are paying our electrical bills to
the power utility companies based on the
amount of electric energy we consumed over a
certain period of time. On top of all, we should
realize that the useful output of our system is
non-electrical form.
Power and Energy
 We define power as the time rate of expending (negative
power) or absorbing (positive power) energy.
P=dw/dt, in watts (W)
 The sign can be either positive or negative.
+ve: The element is absorbing or dissipating (special
case for a resistor) o or receiving power.
-ve: The element is supplying or developing or
expending or delivering or releasing power.
Ideal Basic Circuit Element
Definition:
Ideal – to imply that the element cannot
exist as a realizable physical component.
The purpose of its prescription is to model
actual devices and systems.
Basic – to imply that the circuit cannot be
subdivided or further reduced into smaller
parts.
Ideal Basic Circuit Element
Types of Basic Circuit Element:
Passive – elements are not capable of
generating electrical energy.
 Resistor (dissipates energy)
 Capacitor and Inductor (can store or release energy)
Active – elements capable of generating
electrical energy.
 Voltage source
 Current source
Ideal Basic Circuit Element
Linear resistor:
 Resistor is passive element that dissipates
electrical energy. Linear resistor is the resistor
that obeys Ohm’s law.
Capacitor:
 Capacitor is passive element designed to store
energy in its electric field. It is normally used in
tuning circuits of radio receivers and s dynamic
memory elements in computer systems.
Ideal Basic Circuit Element
Inductor:
 Inductor is another passive element designed to
store energy in its magnetic field. Its numerous
applications can be found in electronic and
power systems such as power supplies,
transformers, radars and electric motors.
Ideal Basic Circuit Element
Voltage source
 Independent source
This source maintains a specified voltage
between its terminals but has no control on the
current passing through it. The symbol of the
independent voltage source is a plus-minus sign
enclosed by a circle.
Ideal Basic Circuit Element
 Dependent voltage source
This kind of voltage source has a specified
voltage between its terminals but it is
dependable on some other variable defined
somewhere in the circuit. The symbol for the
dependent voltage source is a plus-minus sign
enclosed by a diamond shape. The value of the
dependent current source is KVx
(dimensionless) or Kix (ohms) where K is the
scale factor or gain.
Ideal Basic Circuit Element
Current source
 Independent current source
This source maintains a specified current
through its terminals but has no control on the
voltage across its terminals. The symbol of the
independent current source is an arrow
enclosed by a circle.
Ideal Basic Circuit Element
 Dependent current source
This kind of current source has a specified
current between its terminals but it is dependent
on some other variable defined somewhere in
the circuit. The symbol for the dependent current
source is an arrow enclosed by a diamond
shape. The value of the dependent current
source is KVx (in Siemens) or Kix
(dimensionless) where K is the scale factor or
gain.
Kirchhoff’s Laws
Kirchhoff’s Current Law
 Kirchhoff’s Current Law (KCL) states that the
algebraic sum of current entering a node must
be equal to that of leaving the same node.
 Applying KCL, we obtain;
i2 + i6 = i1 + i3 + i4 + i5
i3
i4
i2
i1
i5
i6
Kirchhoff’s Laws
Kirchhoff’s Voltage Law (KVL)
 Kirchhoff’s Voltage Law states that the algebraic
sum of voltage drop in a loop must be equal to
that of voltage rise in the same loop. Stated it in
a different way is that the algebraic sum of all
voltages around a loop must be zero.
 Applying KVL, we obtain;
Loop 1: V1 + V2 + V3 = Vs
Loop 2: V4 + VIs = V2
+ V1 -
+ V4 -
R2
R3
- V3 +
Y
V
y 1
y
0
R4
Loop 2
Is
+ VIs -
Vs
Loop 1
+ V2 -
R1