Fundamental Of Electric Circuit

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In this article we will be discussing the fundamental of Electric circuit. So if you are searching this kind of article, yes you are in the right place.

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INTRODUCTION

Electric circuit theory and electromagnetic theory are the two fundamental theories upon which all electrical engineering are built. Many branches of electrical engineering, such as power, electric machine, control, electronics and many more are based on electric circuit theory. Therefore, the basic electric circuit theory course is the most important course for an electrical engineering students, and always an excellent starting point for a beginning student in electrical engineering education. Now to the main point.

ELECTRIC CIRCUIT

An electric circuit is an interconnection of electrical elements. Or an electric circuit is a closed loop through which electricity flow. In any of the two you use is correct.

A simple electric circuit is shown below. It consists of four basic components: a battery, a light bulb, a switch, and a connecting wires.

Such a simple circuit can exist by itself; it has so many applications, such as a torch light a search light, and so forth.

Electric circuit are used in numerous electrical systems to accomplish different tasks. Our objective in this book is not the study of the various uses and application of circuit. Rather our major concern is the analysis of the circuit. By the analysis of a circuit, we mean a study of the behavior of the circuit: How does it respond to a given input? How do the interconnection elements and devices in the circuit interact?

CHARGE AND CURRENT

The concept of electric charge is the basic principle for explaining all electrical phenomena. And also the most basic quantity in an electric circuit is the electric charge. We all experience the effect of electric charge when we try to remove our wool sweater and have it stick to our body or walk across a carpet and receive a shock.

Charge is an electrical property of the atomic particles of which matter consists. Or charge is a fundamental property of matter that describes the electrical properties of particles.

All matter is made up of fundamental building blocks known as atoms, each of this atom consist of electrons, protons, and neutrons. Charge e on an electron is negative and equal in magnitude to 1.602×10־ while the proton carries a positive charge of the same magnitude as an electron. The presence of equal proton and electron leaves an atom neutrally charge.

Note the following point down about electric charge:

1. The coulomb is a large unit for charge. In 1 C of charge, there are 1÷1.602×10-¹⁹ = 6.24×10¹⁸ electrons. It can be measured in pC, nC, or µC.
2. The only charges that occur in nature are integral multiples of the electronic charge e = –1.602×10-¹⁹
3. The law of conservation of charge state that charge can neither be created nor destroyed, only transferred. Thus the algebraic sum of the electric charges in a system does not change.

ELECTRIC CURRENT

Electric current is the time rate of change of charge. Or current is the flow of electric charge through a conductor, such as wire.

Mathematically, the relationship between current I, charge q, and time t is

I = dq/dt

Where current is measured in amperes (A) and 1 ampere = 1 coulomb/second.

The charge transferred between time t0 and t is obtained by integrating both side of Eq. above. We obtain

q = ʃ I d t

There are two types of current:

Direct current (DC): The current does not change with time, it is constant.

Alternating current(AC): Is the current that varies sinusoidally with time.

EXAMPLE 1. How much charge is represented by 4,600 electrons?

Solution:

Each electron has −1.602 × 10−19 C. Hence 4,600 electrons will have −1.602 × 10−19 C/electron × 4,600 electrons = −7.369 × 10−16 C

EXAMPLE 2. The total charge entering a terminal is given by q = 5t sin 4πt mC. Calculate the current at t = 0.5 s.

Solution

I = dq /dt = d/ dt (5t sin 4πt) mC/s = (5 sin 4πt + 20πt cos 4πt) mA

at t = 0.5,

I = 5 sin 2π + 10π cos 2π = 0 + 10π = 31.42 mA

EXAMPLE 3. Determine the total charge entering a terminal between t = 1 s and t = 2 s if the current passing the terminal is I = (3t 2 − t) A.

Solution:

q = ʃ 2 t=1 I dt = ʃ2 1 (3t 2 − t) dt = (t 3 − t²/2) │2 1 = (8 − 2) – (1 – 1/ 2) = 5.5 C.

VOLTAGE

Voltage (or potential difference) is the energy required to move a unit charge through an element. Or is the measure of the electric potential energy per unit charge in a circuit.

Current and voltage are the two basic variables in electric circuits. The common term signal is used for an electric quantity such as a current or a voltage (or even electromagnetic wave) when it is used for conveying information. Engineers prefer to call such variables signals rather than mathematical functions of time because of their importance in communications and other disciplines. Like electric 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. A dc voltage is commonly produced by a battery; ac voltage is produced by an electric generator.

Keep in mind that electric current is always through an element and that electric voltage is always across the element or between two points.