電路與電子技術(shù)：Chapter-1 Introduction

1、Electrical Engineering Principles & Application電電路與電電子技術(shù)術(shù) Spring 2014 Textbook:Electrical Engineering-principles and Electrical Engineering-principles and applicationsapplications （Fourth EditionFourth Edition），）， Allan R. Allan R. HambleyHambley Reference: 電路分析基礎(chǔ)電路分析基礎(chǔ)，李瀚蓀編，高等教育出，李瀚蓀編，高等教育出版社版社

2、Chapter 1 Introductionoverview1.Recognize interrelationships of electrical engineering with other fields of science and engineering.2. List the major subfields of electrical engineering.3. List several important reasons for studying electrical engineering.4. Define current, voltage, and power, inclu

3、ding their units.5. Calculate power and energy, as well as determine whether energy is supplied or absorbed by a circuit element.6. State and apply basic circuit laws.7. Solve for currents, voltages, and powers in simple circuits.Electrical systems have two main objectives: To gather, store, process

4、, transport, and present information To distribute and convert energy between various formsElectrical Engineering SubdivisionsCommunication systemsComputer systemsControl systemsElectromagnetics Electronics Photonics Power systems Signal processingmechanics+electronics = mechatronicsautomobile elect

5、ronic systemWhy Study Electrical Engineering? To pass the Fundamentals of Engineering (FE) Examination So you can lead projects in your own field To be able to operate and maintain electrical systems To communicate with electrical engineering consultantsCircuits, Currents, Voltages An electrical cir

6、cuit consists of various types of circuit elements connected in closed path by conductors.Electrical Currenttttqdttitqdttdqti0)()()()()(0Electrical current is the time rate of flow of electrical chargethrough a conductor or circuit element. The units are amperes (A), which are equivalent to coulombs

7、 per second(C/s)Direct Current (DC)Alternating Current(AC) When a current is constant with time, we say that we have direct current, abbreviated as dc. On the other hand, a current that varies with time, reversing direction periodically, is called alternating current, abbreviated as ac.VoltagesThe v

8、oltage associated with a circuit element is the energytransferred per unit of charge that flows through the element. The units of voltage are volts (V), which are equivalent to joulesper coulomb (J/C).POWER AND ENERGY21)()()()(ttdttpwtitvtpPassive reference configuration:The current reference enters

9、 the positives polarity ofThe voltageCalculate the power for each element.KIRCHHOFFS CURRENT LAW The net current entering a node is zero. Alternatively, the sum of the currents entering a node equals the sum of the currents leaving a node.A node in an electrical circuit is a point at which two or mo

10、re circuit elements are jointed together. Use KCL to determine the values of the unknown currents .Series circuits:When elements are connected end to end, we say they are connectedin seriesIdentify the groups of circuit elements that are connected in series. KIRCHHOFFS VOLTAGE LAW The algebraic sum

11、of the voltages equals zero for any closed path (loop) in an electrical circuit.loop:A loop in an electrical circuit is a closed path starting at a node and proceeding through circuit elements, eventually returning to the starting node.Parallel circuits:Two circuit elements are connected in parallel

12、 if both ends of one element are connected directly to corresponding ends of each other.Exercise1.9 Use KVL to find the values of and for the following circuit.Exercise1.10 Identify elements that are in parallel/ series in the figure.Circuits ElementsconductorsThe voltage between the ends of an idea

13、l conductor is zero regardless of the current flowing through the conductor.Another term for an ideal conductor is short circuit.voltages sourceAn ideal independent voltage source maintains a specified voltage across its terminals. The voltage across the source is independent of other elements that

14、are connected to it and of the current flowing through it. Ideal circuit elements vs RealityDependent voltage sourceA dependent or controlled voltage source is similar to an independent source except that the voltage across the source terminals is a function of other voltages or current in the circu

15、it. Independent current sourceAn ideal independent current source forces a specified current to flow through itself.Dependent current sourceThe current flowing through a dependent current source is determined by a current or voltage elsewhere in the circuit.Resistors and Ohms LawRiviRvabababConductanceGviRG1Resistance Related to Physical ParametersALRWe want to know the current, voltage, and power for each element.Consider the circuit shown in the following figure. Find the current iR flowing through the resistor. Find the power for ea