ECS203 - handout 1A - wc - Sirindhorn International...

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Sirindhorn International Institute of Technology Thammasat University School of Information, Computer and Communication Technology Lecture Notes: ECS 203 Basic Electrical Engineering Semester 1/2010 Dr.Prapun Suksompong 1 June 16, 2010 1 Special thanks to Dr.Waree Kongprawechnon and Dr.Somsak Kittipiyakul for earlier versions of the notes. Parts of the notes were compiled from C.K. Alexander and M.N.O. Sadiku, Fundamentals of Electric Circuits , 4th ed., McGraw-Hill, International Edition, 2009 and G. Rizzoni, Principles and Applications of Electrical Engineering , 5th ed., Mc-Graw-Hill, International Edition, 2007
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CHAPTER 1 Basic Concepts In electrical engineering, we are often interested in communicating or transferring energy from one point to another. To do this requires an interconnection of electrical devices. Such interconnection is referred to as an electric circuit , and each component of the circuit is known as an element . Definition 1.0.1 . An electric circuit is an interconnection of electri- cal elements. 1.1. Systems of Units 1.1.1 . As engineers, we deal with measurable quantities. Our mea- surement must be communicated in standard language that virtually all professionals can understand irrespective of the country. Such an inter- national measurement language is the International System of Units (SI). In this system, there are six principal units from which the units of all other physical quantities can be derived. 7
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8 1. BASIC CONCEPTS Quantity Basic Unit Symbol Length meter m Mass kilogram Kg Time second s Electric Current ampere A Temperature kelvin K Luminous Intensity candela cd Charge coulomb C One great advantage of SI unit is that it uses prefixes based on the power of 10 to relate larger and smaller units to the basic unit. Multiplier Prefix Symbol 10 12 tera T 10 9 giga G 10 6 mega M 10 3 kilo k 10 - 2 centi c 10 - 3 milli m 10 - 6 micro μ 10 - 9 nano n 10 - 12 pico p Example 1.1.2 . Change of units: 600 , 000 , 000 mm = 1.2. Circuit Variables 1.2.1 . Charge : The concept of electric charge is the underlying prin- ciple for all electrical phenomena. Charge is an electrical property of the atomic particles of which matter consists, measured in coulombs (C). The charge of an electron is - 1 . 602 × 10 - 19 C. The coulomb is a large unit for charges. In 1 C of charge, there are 1 / (1 . 602 × 10 - 19 ) = 6 . 24 × 10 18 electrons. Thus realistic or laboratory values of charges are on the order of pC, nC, or μ C. A large power supply capacitor can store up to 0.5 C of charge. 1.2.2 . Law of Conservation of Charge : Charge can neither be created nor destroyed, only transferred.
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1.2. CIRCUIT VARIABLES 9 Definition 1.2.3 . Current : The time rate of change of charge, mea- sured in amperes (A). Mathematically, i ( t ) = d dt q ( t ) Note: 1 ampere (A) = 1 coulomb/second (C/s). The charge transferred between time t 1 and t 2 is obtained by q = Z t 2 t 1 idt 1.2.4 . Two types of currents: (a) A direct current (DC) is a current that remains constant with time.
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