Objective Questions
Short notes
DC Network theorems help to determine the unknown values of current, resistance and
voltage etc, in electric networks
Electric Circuits and Network Theorems
Different electric circuits (according to their properties) are defined below:
- Circuit. A circuit is a closed conducting path through which an electric current either flows
or is intended flow. - Parameters. The various elements of an electric circuit are called its parameters like resistance,
inductance and capacitance. These parameters may be lumped or distributed. - Liner Circuit. A linear circuit is one whose parameters are constant i.e. they do not change
with voltage or current. - Non-linear Circuit. It is that circuit whose parameters change with voltage or current.
- Bilateral Circuit. A bilateral circuit is one whose properties or characteristics are the same
in either direction. The usual transmission line is bilateral, because it can be made to perform
its function equally well in either direction. - Unilateral Circuit. It is that circuit whose properties or characteristics change with the
direction of its operation. A diode rectifier is a unilateral circuit, because it cannot perform
rectification in both directions. - Electric Network. A combination of various electric elements, connected in any manner
whatsoever, is called an electric network. - Passive Network is one which contains no source of e.m.f. in it.
- Active Network is one which contains one or more than one source of e.m.f.
- Node is a junction in a circuit where two or more circuit elements are connected together.
- Branch is that part of a network which lies between two junctions.
- Loop. It is a close path in a circuit in which no element or node is encountered more than once.
- Mesh. It is a loop that contains no other loop within it. For example, the circuit of Fig. 2.1 (a) has even branches, six nodes, three loops and two meshes whereas the circuit of Fig. 2.1 (b) has four branches, two nodes, six loops and three meshes.
Q) what are two general approaches to network analysis?
(i) Direct Method
Here, the network is left in its original form while determining its different voltages and currents. Such methods are usually restricted to fairly simple circuits and include Kirchhoff’s laws, Loop analysis, Nodal analysis, superposition theorem, Compensation theorem and Reciprocity theorem etc.
(ii) Network Reduction Method
Here, the original network is converted into a much simpler equivalent circuit for rapid calculation of different quantities. This method can be applied to simple as well as complicated networks. Examples of this method are : Delta/Star and Star/Delta conversions. Thevenin’s theorem and Norton’s Theorem etc
Kirchhoff’s Laws
- Kirchhoff’s Point Law or Current Law (KCL)
It states as follows :
in any electrical network, the algebraic sum of the currents meeting at a point (or junction) is zero.
Put in another way, it simply means that the total current leaving a junction is equal to the total
current entering that junction. It is obviously true because there is no accumulation of charge at the
junction of the network. Σ IR + Σ e.m.f. = 0
- Kirchhoff’s Mesh Law or Voltage Law (KVL) : It states as follows : The algebraic sum of the products of currents and resistances in each of the conductors in any closed path (or mesh) in a network plus the algebraic sum of the e.m.fs. in that path is zero.
Objective questions
- Kirchhoff’s current law is applicable to only
(a) closed loops in a network
(b) electronic circuits
(c) junctions in a network
(d) electric circuits. - Kirchhoff’s voltage law is concerned with
(a) IR drops
(b) battery e.m.fs.
(c) junction voltages
(d) both (a) and (b) - According to KVL, the algebraic sum of all
IR drops and e.m.f.s in any closed loop of a
network is always
(a) zero
(b) positive
(c) negative
(d) determined by battery e.m.fs. - The algebraic sign of an IR drop is primarily
dependent upon the
(a) amount of current flowing through it
(b) value of R
(c) direction of current flow
(d) battery connection. - Maxwell’s loop current method of solving
electrical networks
(a) uses branch currents
(b) utilizes Kirchhoff’s voltage law
(c) is confined to single-loop circuits
(d) is a network reduction method. - Point out of the WRONG statement. In the
node-voltage technique of solving networks,
choice of a reference node does not
(a) affect the operation of the circuit
(b) change the voltage across any
element
(c) alter the p.d. between any pair of
nodes
(d) affect the voltages of various nodes.
- c 2. d 3. a 4. c 5. b 6. d