1

ECEN 101
ELECTRIC CIRCUITS I
Instructor:
Dr. Lobna A. Said
Lsaid@nu.edu.eg
Dr. Lobna A. Said 2

Course Information
• Monday and Tuesday
Lectures
According to your schedule

• Eng. Kareem H. Khattab.

Tutorials
Timing according to your schedule

• Eng. Abdulaziz El-Safty.

Labs
Timing according to your schedule
Dr. Lobna A. Said 3

Course Information
Labs
• Lab sessions are one slot/week.
• The complete lab manual is posted on MOODLE.
• You should print the lab manual and bring it with
you each lab.
• It is necessary to go through the lab manual before
attending each lab session.
• A lab report has to be submitted to your lab
instructor at the end of each session.
• The lab instructor will evaluate both your
performance and report.
Dr. Lobna A. Said 4

Course Information

S17
Dr. Lobna

Locations and office Monday

hours

Eng. Kareem UB1-309

Dr. Lobna A. Said 5

Course Information
Dr. Lobna A. Said 6

Course Information
WEEK TOPIC ASSIGNMENT EXAMS PROJECT

I Introduction to Electric Circuits

Assignment 1
II Circuits Elements and Ohm’s Law

III Kirchhoff’s Laws, Voltage and Current Division Rules Quiz 1 Selection

IV The Node-Voltage Method Assignment 2

V The Mesh-Current Method and Source Transformation Milestone 1

VI Revision

VII Superposition method Milestone 2

VII Midterm Exam Assignment 3

IX Thevenin’s and Norton’s Circuits Quiz 2

X Maximum Power Transfer Theorem Final Discussion

XI Energy Storing Elements

Assignment 4
XII Transient Response of First-order Circuits

XIII Revision Assignment 5 Quiz 3

Dr. Lobna A. Said 7

Course Information
Course Assessment
Grading Item Percentage
Attendance 5%
Lab Reports 10%
Lab Exam 5%
Course Project 10%
Assignments 10%
Quizzes (2 out of 3) 15%
Midterm 20%
Final 25%
Dr. Lobna A. Said 8

Course Information
Dr. Lobna A. Said 9

Course Information
References:
1) Charles K. Alexander and Matthew Sadiku,
“Fundamentals of Electric Circuits ”, 5th
Edition, McGrawHill, 2013.
2) J. W. Nilsson and S. A. Riedel, “Electric
Circuits”, 9th Edition. Upper Saddle River,
NJ: Prentice Hall, 2011.
3) J.A. Svoboda and R.C. Dorf , “ Introduction
to Electric Circuit”, Wiley, 9th edition
Dr. Lobna A. Said 10

Course Information
Course Announcements
Assignments must be submitted through Moodle in the
announced deadline. (No Hand submission or emails)
Quizzes and Midterm dates will be announced a week
before it took place.
Absence percentage should not exceed 20% of the
course, otherwise you will be forbidden from entering
the final exam.
In the final exam, you must get 40% of the paper grade
or you will fail in the course regardless of your course
work.
Dr. Lobna A. Said 11

Course Contents
1) Introduction to Electric Circuits.
2) Basic Laws of Electric Circuits.
3) Techniques of Circuit Analysis
4) Energy Storing Elements.
5) Transient Response of First Order
Circuits.
Dr. Lobna A. Said 12

Rules in Lectures
Dr. Lobna A. Said 13

Importance of Electric Circuits

The electric circuit theory provides an important foundation
for learning in your later courses and as a practicing engineer.
It plays an important rule in many electrical engineering
applications such as:

Satellite Telephones
Computers
communication

Medical
Televisions Power lines
equipment
Dr. Lobna A. Said 14

Importance of Electric Circuits

Dr. Lobna A. Said 15

Importance of Electric Circuits

Circuits Elements

Microcontroll Microproces
LDR IC’s ers sor

Battery Arduino Transistor Led

Diode Capacitor Inductor Resistor

Dr. Lobna A. Said 16

Course Objectives
Introducing the models, the mathematical techniques
of circuit theory.

Building and analyzing electric circuits.

Focusing on the problem-solving skills and practical

applications.

The ability to model actual electrical systems with

ideal circuit elements makes circuit theory extremely
useful to engineers.
Dr. Lobna A. Said 17

LECTURE 1

Introduction to Electric Circuits

Dr. Lobna A. Said 18

Systems of Units
Table 1. Basic units
It is important to
have a standard Quantity Basic Unit Symbol
language that all
professionals can Length meter m
understand,
irrespective of the Mass kilogram kg
country where the
Time second s
measurement is
conducted Electric current ampere A
Thermodynamic
The International kelvin K
Temperature
System of Units
(SI) was adopted Luminous
by the General candela cd
intensity
Conference on
Weights and Amount of
mole mol
Measures in 1960. substance
Dr. Lobna A. Said 19

Systems of Units
• The SI unit uses prefixes based on the power of 10
to relate larger and smaller units to the basic unit.
Table 2. SI Prefixes.
Multiple Prefix Symbol
1012 tera T
109 giga G
106 mega M
103 kilo k
10−2 centi c
10−3 mili m
10−6 micro µ
10−9 nano n
10−12 pico p
10−15 femto f
Dr. Lobna A. Said 20

Electric circuits
• Electric circuits are models of electrical systems.
• An electric circuit is an interconnection of electrical
elements linked together in a closed path so that an
electric current may flow continuously.
• An ideal circuit component is a mathematical model of
an actual electrical component, such as the below
battery connected to the light bulb.
Dr. Lobna A. Said 21

Circuit variables
Current (𝒊)

Voltage (𝒗)
Basic Power (𝒑)
Variables

Energy(w)
Dr. Lobna A. Said 22

Circuit variables
Connecting a conducting wire (consisting of several atoms) to a battery
(a source of electromotive force), the charges are forced to move which
creates current.
Electric current (𝒊) :is the time rate of change of charge, measured in
amperes (A).
𝑑𝑞
𝑖= ,
𝑑𝑡
The unit of current :is the ampere (A). An ampere is 1 coulomb per
second.
It is conventional to take the current flow as the movement of positive charges.
That is, opposite to the flow of negative charges.
Dr. Lobna A. Said 23

Circuit variables
Types of current:
A direct current (dc) is a current
that remains constant with time.

Uses: batteries and some special

generators .
An alternating current (ac) is a
current that varies sinusoidally
with time.

Uses: in household to run the air-

conditioner, refrigerator, washing
machine, and other electric
appliances.
Dr. Lobna A. Said 24

Circuit variables
Example 1:
The total charge entering a terminal is given by: 𝑞 =
5𝑡𝑠𝑖𝑛 4𝜋𝑡 𝑚𝐶. Calculate the current at 𝑡 = 0.5𝑠.
Solution:
𝑑𝑞
𝑖= = 5𝑠𝑖𝑛 4𝜋𝑡 + 20𝜋𝑡𝑐𝑜𝑠 4𝜋𝑡 𝑚𝐴,
𝑑𝑡
At 𝑡 = 0.5𝑠,
𝑖 = 5𝑠𝑖𝑛 2𝜋 + 10𝜋𝑐𝑜𝑠 2𝜋 𝑚𝐴 = 31.4159𝑚𝐴.
Example 2 :
The charge flowing in a wire is plotted
in the shown Figure. Sketch the
corresponding current.
Dr. Lobna A. Said 25

Circuit variables
Solution:
𝑑𝑞
𝑖= = slope of 𝑞 𝑣𝑒𝑟𝑠𝑢𝑠 𝑡
𝑑𝑡

15 − 0 10−9
−6
= 7.5x10−3 𝐴 , 0 ≤ 𝑡 ≤ 2µ𝑠
2 − 0 10
0 2µ𝑠 ≤ 𝑡 ≤ 4µ𝑠
𝑖=
15 − 0 10−9
−6
= −5x10−3 𝐴 , 4µ𝑠 ≤ 𝑡 ≤ 7µ𝑠
4 − 7 10
0, 𝑡 ≥ 7µ𝑠

The charge transferred between time 𝑡0 and t is

obtained by integrating both sides of the current
equation to be:
𝑡
𝑞 𝑡 − 𝑞(𝑡0 ) = ‫𝑡𝑑𝑖 𝑡׬‬.
0
Dr. Lobna A. Said 26

Circuit variables
Example 3:
The current flowing through an element is:
4𝐴, 0<𝑡<1
𝑖=ቊ 2
4𝑡 𝐴, 𝑡>1
Calculate the charge entering the element from 𝑡 = 0
to 𝑡 = 2 s.
Solution:
1 2
𝑞 = න 4𝑑𝑡 + න 4𝑡 2 𝑑𝑡,
0 1
2
4 3
1 4
𝑞 = 4𝑡 ቚ + 𝑡 ቤ = 4 + 8 − 1 = 13.3333𝐶
0 3 1 3
Dr. Lobna A. Said 27

Circuit variables
Example 4:
The current in a circuit element is
plotted in shown Figure. Sketch the
corresponding charge flowing through
the element for t > 0.
Solution:
𝑡
𝑞 𝑡 = න 𝑖 𝑡 𝑑𝑡 + 𝑞(𝑡0 )
𝑡0
𝑡
න 450x10−6 𝑑𝑡 + 0 = 450x10−6 𝑡, 0 ≤ 𝑡 ≤ 80𝑚𝑠
0
𝑡
= න −600x10−6 𝑑𝑡 + 𝑞 80𝑚𝑠 = 84 − 600𝑡 x10−6 , 80𝑚 ≤ 𝑡 ≤ 140𝑚𝑠
80𝑚
𝑡
න 0𝑑𝑡 + 𝑞 140𝑚𝑠 = 0, 𝑡 ≥ 140𝑚𝑠
140𝑚
Dr. Lobna A. Said 28

Circuit variables
To move the electron in a conductor in a particular direction
requires some work or energy transfer. This work is
performed by an external electromotive force (the voltage).
Voltage (or potential difference) is the energy required to
move a unit charge through an element, measured in volts
(V).
𝑑𝑤
𝑣=
𝑑𝑞

Where 𝑤 is energy in joules (J) and 𝑞 is charge in coulombs

(C).
The unit of voltage is the volt(V). 1 volt =1 joule/coulomb
= 1 newton-meter/coulomb.
Dr. Lobna A. Said 29

Circuit variables
Types of voltages:
Like the current, a constant voltage is called a dc voltage and
is represented by V, whereas a sinusoidally time-varying
voltage is called an ac voltage and is represented by 𝑣
The voltage across an element (represented by a rectangular
block) connected to points a and b is 𝑉𝑎𝑏 or 𝑉𝑏𝑎 .
The plus and minus signs are used to define reference direction
or voltage polarity.
𝑉𝑎𝑏 = −𝑉𝑏𝑎
Voltage
drop

Voltage
rise
Dr. Lobna A. Said 30

Circuit variables
Power is the time rate of supplying or absorbing energy,
measured in watts (W).
𝑑𝑤
𝑝=
𝑑𝑡
Where 𝑤 is energy in joules (J) and t is time in second
(s).
Applying Chain Rule:
𝑑𝑤 𝑑𝑤 𝑑𝑞
𝑝= = . = 𝑣𝑖.
𝑑𝑡 𝑑𝑞 𝑑𝑡
The power associated with a basic circuit element is simply
the product of the current in the element and the voltage
across the element.
Dr. Lobna A. Said 31

Circuit variables Circuit element

Passive Sign Convention

When current enters the positive
voltage terminal, the element is
absorbing power (positive power).

When current leaves the positive

voltage terminal, the element is
supplying power(negative power).

The law of conservation of energy in any electric circuit

says that, the algebraic sum of power in a circuit at any instant
of time, must be zero.
(Positive Power) + (Negative Power) = 0
Dr. Lobna A. Said 32

Circuit variables
Example 5:
Calculate the power delivered or absorbed by each
element in the following circuit.
Show that the sum of the delivered power = sum of the
absorbed power.
Dr. Lobna A. Said 33

Circuit variables

Solution:
P(absorbed):elements a,c,d,f
𝑝 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 = 10 + 14 + 9 + 36 + 40 = 109
P(supplied):elements b,e,g
𝑝 𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 = −3 − 100 − 6 = −109
Dr. Lobna A. Said 34

Circuit variables
Example 6:
The Figure shows a circuit with five elements. If p1 =
− 205W, p2 = 60W, p4 = 45W and p5 = 30W ,
calculate the power p3 received or delivered by element
3.
Solution:.
𝑝 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 = 60 + 45 + 30 = 135,
𝑝 𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 =-205,
To achieve (Positive Power) + (Negative Power) = 0 ; p3
must be received power and it is equal to 70.
Dr. Lobna A. Said 35

Circuit Elements
Circuit Elements

Passive elements
Active elements
cannot generate
can generate energy
energy

Capacitors and
Inductors Voltage and
Resistors
current sources
(They store energy)
Dr. Lobna A. Said 36

Assignment
I is posted
on Moodle

Check the Deadline

Dr. Lobna A. Said 37

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