Introduction

Basic Concept (Chapter 1)

Any engineering courses related with electricity must study and understand the fundamentals of electric circuits as students enter in their major subjects.

Fundamentals of Electric Circuits

Introduction

Electric circuit and electromagnetic theories are two fundamental theories upon which all branches of electrical engineering are built.
WHY DO WE NEED TO STUDY "BASIC ELECTRIC CIRCUIT"?

•  This is because everything starts with the BASICS. We cannot jump up to the hardest fields without dwelling with the penny matters. Basic electric circuit is the most important course for electrical engineering students and even electronics and computer engineering courses education.
• This is valuable for students like us who are specializing in other branches of the physical sciences because circuits are good model for the study of energy systems in general, and because of the applied mathematics, physics, and topology involved.

What is Electric Circuit?

Fig. 1

An Electric Circuit is an interconnection of electrical elements. Electric circuit theory and electromagnetic theory are the two fundamental theories upon which all branches of electrical engineering are built.
Its function is to transfer energy from one point to another or from one element to another element.

 Fig. 1 This is an example of a simple Electric Circuit. It has battery, switch and the bulb. When you turn on the switch with a closed loop the current flows and the bulb will light up.

---

BASIC ELEMENT

Charge- q(t)

It refers to the basic quantity in an electric circuit.
ELECTRICAL PROPERTY OF MATERIALS

• Exist (Electron) which is negative and (Proton) positive
• Measured in Coulombs (C)C
• One electron has a charge of -1.602 * 10 ^-19 C

Current- i(t)

• It refers to the charge flow rate
• It is measured in Ampere (A)
• 2 types: DC (Direct Current) and AC (Alternating Current)

Voltage- v(t)

• It refers to the charge rate of doing work
• Energyrequired to move a unit charge through an element
• Measured in volts (V)

Power- p(t)

• It refers to time rate of doing work
• Measured in watts (w)

Power can be absorbed or supplied by circuit elements

• positive power- element absorbs power
• negative power- element supplies power
• 'sign' determined by voltage and current
• An ideal circuit is ΣPsupplied + ΣPabsorbed = 0

Energy

It is the capacity to do work

Circuit Elements

• An element is the basic building block of a circuit
• Electric circuit is interconnecting of the elements

      Types of Elements:

• Active elements- capable of generating energy
• Passive elements- absorbs energy

Source

• Independent Source- does not depend to other elements to supply voltage or current.
• Dependent Source- Depend to other elements to supply Voltage or Current.

---

Example Exercises (1)

• Determine the current flowing through an element if the charge flow is given by:   q(t) = (9t² +2t-2) C

Solution:
q(t)= 9t²+2t-2  C
dq/dt= 18t+2
i(t)=dq/dt =18t+2

---

• Find the charge q(t) flowing through a device if the current (i(t)) = (2t + 5) mA and q(0)=0

Solution:
i= dq/dt                                                  q(0)=0
∫dq= ∫i dt                                               q(0)= t²+5t+C =0
q= ∫i dt                                                           =0²+5(0)+C
q= ∫ (2t+5) dt                                                =0
q(t)= t²+5t+C                                                   Therefore, the charge is 0.

---

• The change entering a certain element is shown. Determine the current at:

(a) t = 1 ms
(b) t = 6 ms
(c) t = 10 ms

Solution:
(a) At t = 1ms, i= dq/dt
=80/2
=40A
(b) At t = 6ms, i= dq/dt
=0A
(c) At t = 10ms, i= dq/dt
=80/4
=20A

---

---

---

LEARNING/SUMMARY

• In analyzing or dealing with circuits, it is really better for us to know what are the concepts under every thing. We must know how everything works, how each element affects the whole circuits and how conscious we should be in taking part of analyzing the circuit. Because if we fail to do this, we will be failure at all level regarding circuit analysis.

• It is important to know the basic elements of the circuit because it is always the best to start with the basics since it is the foundation in solving or dealing problems as we go through our journey to be electrical and electronics engineers.

• Each element is co-related with one another. They might be directly proportional or inversely proportional with each other.