CHETTINADCOLLEGE OF ENGINEERING AND TECHNOLOGY-KARUR
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
I YEAR / II SEM
UNIT II-NETWORK THEOREMS FOR DC AND AC CIRCUITS
2 MARKS
1.What is network analysis?
The means to find a current through or voltage across any branch of network or circuit is called network analysis.
2.What is datum node?
In a network one of the node is assumed as reference node for analysis whose potential is assumed to be zero .It is called zero potential node or datum node.
3.What are the basic network theorems?
1.Superposition theorem
2.Maximum power transfer theorem
3.Thevenin’s theorem
4.Norton theorem
5.Millman’s theorem
6.Tellegan’s theorem.
7.compensation theorem.
8.Reciprocity theorem
9.Substitution theorem.
4.State the superposition theorem. Nov 04
In a linear bilateral network containing more than one sources is the sum of the responses produced by the sources, each acting independently. The response means the voltage across the element or the current in the element.
5.State whether the superposition theorem is applicable to power in a circuit? Why?
The superposition theorem is not applicable to power in a circuit because the power is proportional to square of the current, which is not a linear function.
6.State Thevenin’s theorem Nov 04,May 04
Any linear bilateral complex circuit can be represented by a single voltage equivalent (Thevenin’s voltage) VTH with a series impedance (Equivalent impedance) ZTH.
7.State the limitations of Thevenin’s theorem.
Not applicable to the circuits consisting of nonlinear elements.
Not applicable to unilateral networks.
There should not be magnetic coupling between the load and circuit to be replaced by Thevenins theorem.
In the load side, there should not be controlled sources, controlled from some other part of the circuit.
8. State Norton’s theorem Nov 05
Any linear bilateral complex circuit can be represented by a single current source (Norton’s current )in parallel with an equivalent impedance ZTH in parallel.
9.What is other name for Norton’s theorem?
It is the dual of Thevenin’s theorem.
10.State maximum power transfer theorem.
In an active network, maximum power transfer to the load takes place when the load impedance is the complex conjugate of an equivalent impedance of the network as viewed from the terminals of the load.
11.State the reciprocity theorem. May 06,Nov 05
Any linear network consisting of linear and bilateral impedances and active sources, then ratio of voltage V introduced in one loop to the current I in other loop is same as the ratio obtained if the positions of V and I are interchanged in the network.
12.How the sign conventions are done?
The sign conventions are done using the
Kirchoff’s current law
Kirchoff’s voltage law
13.When will be the nodal method is advantageous?
The nodal method is advantageous when there are more number of branches in parallel in a network.
14.State the formula for Equivalent impedance
Zeq = VTH
ISC
15.Will the method of calculating the Zeq differ between theorems?
No the method of calculating the Zeq differs between theorems because circuit impedance never changes for dependant source network.
16.State the corollary of Maximum power transfer theorem
If only magnitude of ZL is varied but its angle cannot be varied , then the maximum power transfer takes place if absolute magnitude of ZL is made equal to the absolute magnitude of Zeq .This is corollary.
17.State the theorem which is applicable to all type of network
Tellegan’s theorem is valid for any lumped network, which may be linear, or nonlinear, active or passive, time varying or time invariant.
20.Write the maximum power expression
Pmax = V2TH
4RL
Where VTH is Thevenin’s voltage,RL is Load resistance.
21.What is the condition for Maximum power transfer in D.C circuits? Apr 04
Power transfer from a DC source network to a resistive network is maximum when the internal resistance of the Dc source network is equal to the load resistance
Load resistance = internal resistance of source
In AC network load impedance = Complex conjugate of the source impedance
22. What is the condition for Maximum power transfer in A.C circuits? Apr 04
In AC network load impedance = Complex conjugate of the source impedance
23.What is the application of Maximum power transfer Theorem?
This theorem is used to find the value of load resistance for which there would be maximum amount of power transfer from source to load.
24.What is the efficiency of the circuit during Maximum power transfer?
During maximum power transfer the efficiency becomes =50%
25.Write the total power supplied equation while using Maximum power transfer
Total power supplied P = Vo2 / (2 RTH)
Where VO is Input voltage,RTH is Thevenin’s resistance
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
I YEAR / II SEM
UNIT II-NETWORK THEOREMS FOR DC AND AC CIRCUITS
12 MARKS:
1.Explain in detail about the different methods of Finding RTH
Reference book: Circuit Theory by A.Chakrabarti P.No.326,979
2. State and Explain Thevenin’s theorem. Nov 05
Reference book: Circuit Theory by A.Chakrabarti P.No.:325,979
3. Explain in detail about Norton’s theorem
Reference book: Circuit Theory by A.Chakrabarti P.No.:345,980
4. Explain in detail about Superposition’s theorem
Reference book: Circuit Theory by A.Chakrabarti P.No.:364,995
5. Explain in detail about the procedure used in Maximum power transfer theorem Apr 04, Nov 05
Reference book: Circuit Theory by A.Chakrabarti P.No.:374,1008
6.Find the Thevenin equivalent circuit of the circuit shown to left of the terminals ab. Then find the current through RL = 16 and 36 . May 06
7. Find the value of RL for maximum power transfer in the circuit. Find the maximum power. May 06
8.Determine the Thevenin’s equivalent circuit Nov 04
9.Verify superposition theorem for the (2+j5) impedance. Nov 04
10.Determine the maximum power delivered to the load in the circuit. Nov 04
11.Find the Norton’s equivalent at terminals AB in the circuit. Nov 03
12.Using superposition theorem calculate current through (2+j3) impedance branch of the circuit shown. Nov 05
13.Find the current through branch ab of the network using Thevenin’s theorem. Nov 05
14.Verify Reciprocity theorem. Apr 04
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
I YEAR / II SEM
UNIT II-NETWORK THEOREMS FOR DC AND AC CIRCUITS
GLOSSARY
Thevenin’s theorem is most commonly used network theorem.
Thevenin’s theorem is desired to determine the current through or voltage across any element in a network without going through the rigorous method of solving a set of network equations
Steps for solving a network Utilizing Thevenin’s theorem
1.Remove the load resistor (RL) and find the open circuit voltage VO.C across the open circuited terminals
2.Deactivate the constant sources and find the internal resistance (Thevenin’s resistance) of the source side looking through the open circuited load terminals. Let this resistance be RTH
3.Obtain Thevenin’s equivalent circuit by replacing RTH in series with VO.C
4.Reconnect RL across the load terminals
VO.C
IL Load current = ------
RTH + RL
Steps for solving a network Utilizing Norton’s theorem
- Remove the load resistor (RL) and find the internal resistance of the source network by deactivating the constant sources. Let this be Rint
- Short the load terminals and find the short circuit current flowing through the shorted load terminals using conventional network analysis. Let this be i S.C
- Norton’s equivalent circuit is drawn by keeping Rint in parallel to i S.C
- Reconnect the load resistor (RL) across the load terminals and the current through it IL is given by
Rint
IL Load current = i S.C ------
Rint + RL
Superposition Theorem finds use in solving a network where two or more sources are present and connected in series or parallel
Maximum power transfer theorem is used to find the value of load resistance for which there would be maximum amount of power transfer from source to load
Reciprocity theorem is onlyapplicable to single source networks and not in multi source network
Steps for solving a network Utilizing Norton’s theorem
1.The branches between which the reciprocity is to be established are to be selected first
2.The current in the branch is obtained using conventional network analysis
3.The voltage source is interchanged between the branches concerned
4.the current in the branch where the voltage source existed earlier is calculated
The term independent source indicates that the magnitude of the source is independent of the network to which it is applied and that it exhibits its terminal characteristics even if completely isolated.
A dependent or controlled source is that whose magnitude is governed by a current or voltage of the system which it is situated