1. Chapter1. Circuit Concept Network: The interconnection of two or more simple circuit elements is called an electric network. Fig1. Network Circuit: If a network contains at least one close path, it is termed an electric circuit. It follows then that every circuit is a network but all networks are not the circuits. Fig2. circuit

2. Chapter1. Circuit Concept Active Network: a network containing at least one active element such as independent voltage or current source is called an active network. Fig3. Active Network

3. Chapter1. Circuit Concept Passive Network: a network which does not contain any active element is called a passive network. Fig3. Passive Networks

4. Chapter1. Circuit Concept Branch of the network: A circuit element in a network may be called the branch of a network. Sometimes, all those elements which are connected in series such that identically the same current flows through them can be said to constitute a branch.

5. Chapter1. Circuit Concept Node: A point in a network where two or more circuit elements meet is termed as node. In fig4 1, 2 & 4 are nodes. Principal Node : A point in a network where three or more circuit elements meet is called a principal node. In Fig4. 2 & 4 are principal nodes. Terminal Node : Terminal of a branch not connected anywhere is called a terminal node. In Fig4. 3 & 5 are terminal nodes. Fig4. For understanding of different nodes

6. Chapter1. Circuit Concept Loop: A close electrical path in the network is called a loop. Mesh : A close electrical path which does not enclose any other close path inside it is called a mesh. Thus all meshes are the loops, but not all loops are the meshes. In Fig.5 ABEFA & BCDEB are meshes & loops, whereas ABCDEFA is a loop but not a mesh. Fig5. For understanding of mesh & loop

7. Chapter1. Circuit Concept CLASSIFICATION OF NETWORKS Classification of the networks depends upon 1.The kind of elements of which the network is composed of & on the basis of their properties 2.In terms of the general properties of its responses to excitation applied to its input terminals Network Classification Linear & Nonlinear Networks Time invariant & time variant Networks Active & Passive Networks

8. Chapter1. Circuit Concept LINEAR NETWORKS & LINEARITY →In a linear network, the voltage & current relationship is described by a linear equation. →Suppose network is under relaxed condition i.e the initial condition is zero and an excitation e 1 (t) is applied for which the response is c 1 (t) & for excitation e 2 (t), the response is c 2 (t). Then the network is classified as linear if for excitation e 1 (t)+ e 2 (t), the response is c 1 (t)+ c 2 (t). This shows that that a linearity follows super position theorem. →The validity of the principal of superposition means that the presence of one excitation does not affect the responses due to the other excitations and there are no interactions among the responses of different excitations in the network. →A network is linear if it satisfies the principle of superposition.

9. Chapter1. Circuit Concept TIME-INVARIENT & TIME-VARIENT NETWORK →A network is said to be time-invariant if the network produces the same response to a given excitation irrespective of time of application of excitation. →If the response to an excitation e(t) is c(t), then in time-invariant network, the excitation e(t+t1) will produce a response c(t+t1) where t1 is any time. →This implies that the values of network components are constant at all times and do not change with time in a time-invariant network. →If the parameters vary with time in a network, the network is called a time-varying network.

10. Chapter1. Circuit Concept RECIPROCITY PROPERTY OF THE NETWORK →Some networks have the property that the response produced at one point of the network by an excitation acting at another point is invariant if the positions of excitation and response are interchanged. (with the proper polarities of the excitation & the response functions) 1’1’ V2(t) NETWORK 1 V1(t) 2 2’2’ I2(t) NETWORK 1 1’1’ 2 2’2’ I1(t) If V1(t) = V2(t) Then I1(t) = I2(t) It is called a reciprocal network. Fig6. For understanding Reciprocal Network

11. Chapter1. Circuit Concept LUMPED & DISTRIBUTED NETWORK →Many devices in electrical system are distributed in space e.g transmission lines, windings of transformers or generators are distributed in a way. Whenever these devices are energized, the effect is not experienced by the line length or winding lengths instantly because of finite velocity of electric signals. However, if interest in steady state or terminal quantity, it is sufficient to assume the parameters lumped rather then distributed. →Sometimes, when we are interested in the intermediate values and point to point variation of electric signals, we talk true nature of these devices i.e distributed nature. →Otherwise, we assume the parameters to be lumped.

12. Chapter1. Circuit Concept UNILATERAL & BILATERAL NETWORK →In bilateral element the voltage current relationship is the same irrespective of direction of flow of current in it e.g resistance, inductance, capacitance. →A unilateral element has different voltage-current relations for two possible directions of flow of current i.e diode, rectifier etc.

13. Chapter1. Circuit Concept ACTIVE & PASSIVE COMPONENTS OF NETWORK →Energy source (Voltage or Current sources) are active elements, capable of delivering energy to some external device. →The passive elements are those which are capable only of receiving energy or power. →Some passive elements like inductors & capacitors are capable of storing a finite amount of energy & return it later to an external device. →More specifically, an active element is capable of delivering an average power greater than zero to some external device over an infinite time interval. For example, ideal sources are active elements. →The passive element is defined as one that cannot supply average power that is greater than zero over an infinite time interval e.g. resistor, inductor, capacitor etc. fall in this category.