lecture_1.pdf

Lecture 1 Introduction to Electrical Engineering Lecture 1  Contents Circuit Elements – Active & Passive Elements Sources – Current and Voltage Sources – Ideal & Practical Sources – Independent & Dependent Sources – Refere...

Lecture 1 Introduction to Electrical Engineering Lecture 1  Contents Circuit Elements – Active & Passive Elements Sources – Current and Voltage Sources – Ideal & Practical Sources – Independent & Dependent Sources – Reference Symbols Network & Circuits – Active and Passive Circuits – Reference Directions – Node, Path, Loop and Branch Numerical Examples Lecture 1 2  Circuit Elements Circuit elements are defined based on the mathematical relationship of current through the element and voltage across the element Lecture Lecture21 3  Circuit Elements If the voltage across the element is If the current through the element is proportional to the independent of the volatge current through it, the circuit – Ideal Voltage Source element is dependent on the current or – Resistor voltage elsewhere derivative of the current – Dependent Current Source – Inductor Integral of the current – Capacitor independent of the current – Ideal Voltage Source dependent on the current or voltage elsewhere – Dependent Voltage Source Lecture Lecture21 4  Active & Passive Circuit Elements Active element is an element capable of supplying an average power(>0) for infinite time interval. – Eg. Ideal Sources Passive element is an element incapable of supplying an average power(>0) for infinite time interval. – Eg. Resistor, Capacitor, Inductor – R is a passive circuit element that dissipates energy – C and L are passive circuit elements, having the ability to store and deliver finite amount of energy. Lecture 1 5  Ideal & Practical Sources An ideal source is an active element that supplies specific voltage or current independent of other circuit elements. Lecture 1 6  Ideal & Practical Sources Ideal voltage source Ideal Current source – Voltage remains constant – Current remains constant – Zero internal resistance – Infinite internal in series resistance in parallel Practical voltage source Practical Current source – Modelled as Ideal – Modelled as Ideal voltage source in series current source in parallel with internal resistance with resistance. Lecture 1 7  Ideal & Practical Sources An ideal current source supplies a current of 300mA to a load of 1kΩ. When the load is changed to 100Ω, the load current will be – (a) 3A – (b) 300mA – (c) 30mA – (d) 100mA Solution – (b) 300mA – Current supplied by the ideal current source remains the same and is independent of the load variations. Lecture 1 8  Independent & Dependent Sources Symbols : Independent & Dependent Sources Independent Source – Ideal independent source maintains same voltage or current unaffected byother circuit elements present in the circuit. Dependent Source Dependent source -Classification – A dependent voltage or Voltage Source Current Source current source is one whose Voltage Voltage Controlled Voltage Controlled value is proportional to Controlled Voltage Source Current Source another voltage or current VCVS VCCS in the circuit. Current Controlled Current Controlled Voltage Source Current Controlled Current Source CCVS CCCS Lecture 1 9  Network & Circuits Network & Circuits – Connection between two or more “circuit elements” (passive) – A network with closed path is a network circuit – Every circuit is a network, every network isn’t a circuit Active & Passive Networks – Network with active elements(at circuit least one voltage source or current source) is an active network – Passive network does not contain an active source. active network Lecture 1 10  Reference Directions Voltage – To define voltage across an element, a value and polarity must be given. (the terminals must be labelled with “+” and “-” signs) Current Flow – To define current flow, a value and a direction must be given – “arrow” is used for labelling current directions – Positive Current flow direction, opposite to electron flow direction – Current flows from higher potential to lower potential in passive elements. Current flows from lower potential to higher potential in active elements(Sources). Power Flow – Positive current flows out of positive terminal, the element supplies power. – Positive current flows into the positive terminal, the element absorbs power. Lecture 1 11  Reference Directions: Numerical Example Find the power in the circuit (a),(b) and (c)? Solution (a) Pa = (+2)*(+3) = +6W (b) Pb = (-2)*(-3) = +6W (c) Pc = (+4)*(-5) = -20W Lecture 1 12  Network Terminologies Node : – Point of connection between 2 or more “circuit elements” Branch – A single path in a network – With 1 simple element and node at each end Path : – While moving from one node to another, no nodes are encountered more than once. Closed Path/Loop – A loop is a closed path in a network formed by no of connected branches – Starting node = Ending node Mesh – Mesh is a loop that contains no other loop within it. Lecture 1 13  Network Terminologies: Numerical Example Find the number of meshes, nodes and loops in the circuit below? Solution (a) No of Meshes =3 (b) No of loops = 6 (c) No of nodes = 3 Lecture 2 14  References Edward Hughes. “Electrical and Electronic Technology”, 10th Edition, Pearson Education Asia, 2011. William H. Hayt Jr. ,Jack E Kemmerly, Steven M Durbin, “Engineering Circuit Analysis”, 6th Editions, Tata McGraw Hill Publishing Company Vincent Del Toro, ‘Electrical Engineering Fundamentals’, Second Edition, Prentice Hall of India Private Limited, 2003 Lecture 1 15 Thank You Lecture 1 16