circuit theory 2-marks

SKR ENGINEERING COLLEGE 2 MARKS Q & A

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERINGDEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

SUBJECT CODE : EE 2151

SUBJECT NAME : CIRCUIT THEORY

SEMESTER : I I

YEAR : 2012 - 13

Handled by

Mr. K. Jagadish Babu

EE2151 CIRCUIT THEORY LT P C 3 1 0 4 (Common to EEE, EIE and ICE Branches)


UNIT I BASIC CIRCUITS ANALYSIS 12Ohm’s Law – Kirchoffs laws – DC and AC Circuits – Resistors in series and parallel circuits – Mesh current and node voltage method of analysis for D.C and A.C. circuits.

UNIT II NETWORK REDUCTION AND NETWORK THEOREMS FOR DC AND AC CIRCUITS 12Network reduction: voltage and current division, source transformation – star delta conversion.Thevenins and Novton & Theorem – Superposition Theorem – Maximum power transfer theorem – Reciprocity Theorem.

UNIT III RESONANCE AND COUPLED CIRCUITS 12Series and parallel resonance – their frequency response – Quality factor and Bandwidth - Self and mutual inductance – Coefficient of coupling – Tuned circuits – Single tuned circuits.

UNIT IV TRANSIENT RESPONSE FOR DC CIRCUITS 12Transient response of RL, RC and RLC Circuits using Laplace transform for DC input and A.C. with sinusoidal input.

UNIT V ANALYSING THREE PHASE CIRCUITS 12Three phase balanced / unbalanced voltage sources – analysis of three phase 3-wire and 4-wire circuits with star and delta connected loads, balanced & un balanced – phasor diagram of voltages and currents – power and power factor measurements in three phase circuits.

TOTAL : 60 PERIODSTEXT BOOKS:1. William H. Hayt Jr, Jack E. Kemmerly and Steven M. Durbin, “Engineering CircuitsAnalysis”,Tata McGraw Hill publishers, 6th edition, New Delhi, (2002).2. Sudhakar A and Shyam Mohan SP, “Circuits and Network Analysis and Synthesis”,Tata McGraw Hill, (2007).

REFERENCES:1. Paranjothi SR, “Electric Circuits Analysis,” New Age International Ltd., New Delhi, (1996).2. Joseph A. Edminister, Mahmood Nahri, “Electric circuits”, Schaum’s series, Tata McGraw-Hill, New Delhi (2001).3. Chakrabati A, “Circuits Theory (Analysis and synthesis), Dhanpath Rai & Sons, New Delhi,(1999).4. Charles K. Alexander, Mathew N.O. Sadik, “Fundamentals of Electric Circuits”, Second Edition, McGraw Hill, (2003).

UNIT 1


BASIC CIRCUITS ANALYSIS

1. Define Ohms Law. The potential difference across any two ends of a conductor is directly proportional to the current flowing between the two ends provided the temperature of the conductor remains constant.

2. Define KCL KCL states that the algebraic sum of currents in a node is zero.

3. Define KVL. KVL states that the algebraic sum of voltages in a closed path is zero.

4. Define electric currentThe flow of free electrons in a metal /conductor is called an electric current OrIt is also defined as the rate of flow of free electrons in a conductive or semi conductive medium. The unit of current is ampere or coulomb /seconds .The symbol of current is I .(I = dq / dt or Q/t)

5. Define electric powerThe rate at which work is done in an electric circuit is called electrical powerPower =work done in an electric circuit/timeThe basic unit of electric power is joules /second or watt

6.Define-Electric energyThe total workdone in an electric circuit is called as electrical energy.Electric Energy = power x time = voltage x current x timeThe basic unit of electric energy is watt-sec

7. What is meant by linear and nonlinear elements? Linear elements shows linear characteristic of voltage Vs Current. Nonlinear element the Current passing through it does not change linearly with the linear change in applied voltage at a particular frequency

8. What is meant by active and Passive elements? If a circuit element has the capability of enhancing the energy level of a signal passing thorough it is called an active element. Passive elements do not have any intrinsic means of signal boosting.

9. Unilateral and bi lateral elements If the magnitude of the current passing through an element is affected due to change in the polarity of the applied voltage is called Uni lateral elements. If the current magnitude remains the same even if the applied EMFs polarity is changed is called bilateral elements.

10. Define Voltage or electric potentialThe force which tends to move electrons from one place to other place is called voltage


Electric potential V = Work done /Charge = W / Q

11. What are the types of energy sources.Energy source are classified into two types .They are a.voltage sourceb.Current source In each of the above two,there are again two types namely Idea source and Practical source.

12. Define –ResistanceIt is the property of material/Conductor by virtue of which it opposes the flow of (free ) electrons through the material.Thus the resistance restricts the flow of electric current through the material The unit of resistance (R) is ohm.

13. What are the limitations of ohm’s law?It does not apply /obey to all non-metallic conductorsIt also does not apply to nonlinear devices (zener diodes ,voltage regulator tube etc)It holds good only for constant temperature.

14. Explain-Voltage SourceA Practical voltage source consists of internal resistance in series with source voltage.The terminal voltage across the load changes with change in the load current .It is due to the voltage drop across the internal resistance.

15. What is the advantage of mesh current analysis?Mesh analysis ensures that least possible number of equations of currents ,is used .This greatly simplifies the problem.

16. Explain Ideal voltage sourceThe terminal voltage is independent of current. It is possible only when the internal resistance of an ideal source is zero.

17. Explain - current sourceA practical current source consist of resistance in parallel with source (generator ,battery etc)

18. Explain Ideal Current sourceIts Load current is independent of voltage. It is possible only when R = Infinite..R is open circuit.

19. Explain series combination of resistance.If the resistance is connected end to end then the combination is said to be series .The energy sources connected between the free ends.

20. What are the demerits of series circuits?Any break in any part of the circuit will break /open the current flow through the rest of the circuit. Voltage are additive so it is not suitable for practical lighting loads.

21. What are the concepts of series circuit? The current flowing in all parts of the circuit is same


Voltage across the different elements will depend upon the resistance of elements. Voltage drops, resistance and powers are addictive nature. The applied voltage equals the sum of voltage drops.

22. What are the applications of parallel circuits? All electrical appliances are connected in parallel; each device can be controlled individually with the help of a separate switch.

23. Compare-Series and parallel circuits.Parameter Series circuit Parallel Circuits

CurrentThe current is same through all the elements

The current is divided ,inversely proportional to resistances

VoltageThe voltage is distributed (additive), it is proportional to resistance.

The voltage is the same across each elements in parallel combination

ResistanceThe total resistance equal to the sum of the individual resistance

The total resistance equal to whole reciprocal of the individual resistance

Current flowThere is only one path for the flow of current

There are more than one path for the flow of current.

UNIT – 2

NETWORK REDUCTION AND NETWORK THEOREMS FOR DC AND AC CIRCUITS

1. State superposition theorem. It states that the response of a linear circuit with multiple sources is given by algebraic sum of responses due to individual sources acting alone.

2. State Thevenin’s theorem. It states that any linear bilateral network can be replaced by a single voltage source, Vth , in series with a single impedance, Zth

3. State Norton’s theorem. It states that any linear bilateral network can be replaced by a single Current source, IN, in parallel with single impedance, Zth

4. State max power transfer theorem. In an linear bilateral network containing an independent voltage source in series with resistance Rs deliver maximum power to the load resistance RL when RL = Rs-----dc circuits.

Max. Power is transferred to load impedance if the Load impedance is the complex conjugate of the source impedance. ---AC CIRCUITS

5. State reciprocity theorem.


It states that in a linear, bilateral, single source circuit the ratio of excitation to the response is constant when the position of excitation and response are interchanged.

6. Steps to solve Thevenin’s Theorem • Remove the load resistance and find the open circuit voltage VOC • Deactivate the constant sources ( for voltage source remove it by internal resistance & for current source delete the source by OC ) and find the internal resistance (RTH) of the source side looking through the open circuited load terminals • Obtain the Thevenin’s equivalent circuit by connecting VOC in series with RTH• Re connect the load resistance across the load terminals

7. Steps to solve Norton’s Theorem • Remove the load resistor and find the internal resistance of the source N/W by deactivating the constant source • Short the load terminals and find the short circuit current • Norton’s equivalent circuit is drawn by keeping RTH in parallel with ISC

8. What is the load current in a Norton’s circuit? IL = (ISC. RTH) / ( RTH + RL)

9. What is the load current in a Thevenin’s circuit? IL= VOC /( RTH + RL)

10. What is the max power in a circuit? Max: power = VOC x VOC / 4 RTH

11. What is the power equation of Tellegen’s Theorem? ΣVbIb=0, where b=1 to n

12. Steps to solve Reciprocity Theorem • The branches b/w which reciprocity is to be established is to be selected first• The current in the branch is obtained using conventional n/w analysis• The voltage source is interchanged b/w the branches concerned• The current in the branch where the voltage source was existing earlier is calculated

13. Steps to solve Max: power transfer Theorem • Remove the load resistance and find Thevenin’s resistance• Find the VTH• Max: power is given by VOC2 / 4 RTH

14. Explain the purpose of star to delta and delta to star transformationTransformation of a given set of resistance in star to delta or vice versa proves extremely useful in circuit analysis and the apparent complexity of given circuit can sometimes be very much reduced. 15. What is meant by linear and nonlinear elements?

Linear elements shows linear characteristic of voltage Vs Current. Nonlinear element the Current passing through it does not change linearly with the linear

change in applied voltage at a particular frequency


16. Can the super position theorem be applied to solve electric circuits with diodes present in the circuit? Why?No, because diode is a non-linear device.

17. What are the applications of thevenins theorem? It is applied to all linear circuits. This theorem is useful when it is desired to know the effect of the response in the

network(on varying part of the network)

18. Mention any two advantages of representation of network equation in matrix form. It is easy to slove by matrix representation method compared to other methods. Representations of quantities are quite simple by matrix method and hence complexity is

reduced

19. State equations of DELTA TO STAR & STAR TO DELTA of a network.

DELTA TO STAR

Ra = (Rab x Rac ) / (Rab + Rbc + Rca)

Rb = (Rab x Rbc ) / (Rab + Rbc + Rca)

Rc = (Rca x Rbc) / (Rab + Rbc + Rca)

STAR TO DELTA

Rab = Ra x Rb + Rb x Rc + Rc x Ra / Rc

Rbc = Ra x Rb + Rb x Rc + Rc x Ra / Ra

Rca = Ra x Rb + Rb x Rc + Rc x Ra / Rb

20. Write some application of maximum power transfer theorem. In communication networks In power networks.

21. Limitations of Thevenin’s theorem Not applicable to the circuits consisting of nonlinear elements Not applicable to unilateral elements. There should not be magnetic coupling between the load circuit to replace by thevenins

theorem In the load side, there should not be controlled source, controlled from some other part of

the circuit.

22. Super position theorem is applicable only to Linear network

-----------------------


23. Thevenin’s theorem is useful when the current in one branch of network is to be ----------------------------- determined for Different values of branch resistance

24.Find the equivalent resistance between A and B in the below circuit

In above fig resistors 1 and 1 are in parallel = 1x1 / (1+1) = R1 X R2 /(R1 +R2) = ½ = 0.5 OHM

0.5 OHM and 0.5 ohm are in series = 0.5 +0.5 = 1 ohm

1 and 1 resistors are in parallel = 0.5 ohm

UNIT-3

RESONANCE AND COUPLED CIRCUITS

1. Define quality factor. The quality factor is defined as the ratio of maximum energy stored to the energy dissipated in one period. OrThe ratio between capacitor voltage or inductor voltage at resonance to supply voltage is known as quality factor.

2. What are half power frequencies? In RLC circuits the frequencies at which the power is half the max /min power are called half power frequencies.

3. Define selectivity. It is defined as the ratio of bandwidth and resonant frequency.

4. Write the characteristics of series resonance. a) At resonance impedance is minimum and equal to resistance therefore current is max. b) Before resonant frequency the circuit behave as capacitive circuit and above resonant frequency the circuit will behave as inductive circuit. c) At resonance the magnitude of voltage across inductance and capacitance will be Q times the supply voltage but they are in phase opposition.

5. What is anti-resonance? In RLC parallel circuit the current is min at resonance whereas in series resonance the current is max. Therefore the parallel resonance is called anti resonance.

6. Write the characteristics of parallel resonance.

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a) At resonance admittance is min and equal to conductance therefore the current is min. b) Below resonant frequency the circuit behaves as inductive circuit and above resonant frequency the circuit behaves as capacitive circuit. c) At resonance the magnitude of current through inductance and capacitance will be q times the current supplied by the source but they are in phase opposition.

7. Define-ResonanceIt is a circuit condition at which a RLC circuits behaves as purely resistive circuits ( Inductive reactance should be equal to Capacitive reactance)…Voltage and current should be in phase .i.e. Phase angle voltage and current vector is zero.

8. Define-Anti-ResonanceIn RLC parallel circuits the current is minimum at resonance whereas in series resonance the current is maximum. Therefore the parallel resonance is called anti-resonance.

9. Define the following terms a) cycle b)amplitudeCycle:-One complete set of positive and negative halves constitute a cycle.Amplitude:- The maximum positive or negative value of an alternating quantity is called as the amplitude.

10. Define tuned circuitsCouple circuits can be adjusted to act selectively to one or more frequencies and to reject others .These coupled circuits are known as tuned couple circuits. Tuned circuits are two types 1.single tuned coupled circuits 2.double tuned coupled circuits.

11. Define single tuned coupled circuits.If a capacitor is introduced in the primary part or secondary part of mutually coupled circuits, to tune the frequency of the circuit, it is called as single tuned circuits.

12. Define double tuned circuits.If two capacitors are introduced each one in both primary and secondary part of the mutually coupled circuits, the coupled circuits is called as double tuned circuits.

13. Application of double tuned coupled circuits Double tuned coupled circuits are used in communication systems. It is widely used in IF amplifiers in the receiver. It is used as band pass filter.

14. Define Self-Inductance.When permeability is constant the self-inductance of a coil is defined as the ratio of flux linkage and current.

15. Define Mutual InductanceWhen permeability is constant the mutual inductance between two coupled coils is defined as the ratio of flux linkage in one coil due to common flux and current through another coil.

16. Define Co-Efficient of coupling.In coupled coils the co-efficient of coupling is defined as the fraction of total flux produced by one coil linking another coil.


17. In a series RLC circuit, if the value of L and C are 100 H µ and 0.1 µfrespectively, find the resonance frequency in HZ.Frequency = 1/(2x3.14 (LC)0.5 = 1/(6.28(100HX0.10.1 µf)0.5

18. What is natural frequency?Oscillations are occurred due to the presence of resistance in the circuit. Frequency response of a circuit without resistance results natural frequency and other wise is known as natural frequency of oscillations.

19. Give the relation between bandwidth, resonant frequency and quality factor. Quality factor Q = resonant frequency / bandwidth = ωL / R

20. A series R-L-C circuit has R=500 OHM ,L= 100 micro henry and C=300 pico farad ,V=20 v. What is the current at resonanceThe current at resonance will be I = V / R = 20/80 = 1/4 = 0.25 AMPS.

21. An R-L-C circuit consist of a resistance of 1000 ohm ,an inductance of 100 milli henry and capacitance of 10 micro farad .The Q factor of the circuit is? Q= 1 / R ( L/C)1/2

Q= 0.1

22. A circuit with a resistor, inductor and capacitor in series is resonant of fo Hz.If all the component values are now doubled, what is the values are resonance frequency and quality factor?New frequency = 1 / 2x3.14 (2LX2C ) 0.5

Resonant frequency =1 / 2x3.14 (LXC ) 0.5

new frequency / resonant frequency = ½Similarly new quality factor / quality factor = ½

23. What does series aiding mean. When two coils are connected in series the current enters at dotted end in both the coils and so the self and mutual induced emf will have same polarity. 24. What does series opposing mean. When two coils are connected in series the current enters at dotted end in one coils and leaves at another coil so the self and mutual induced emf will have opposite polarity. 25. What is property of additivity and homogeneity. i) The property of additivity says that the response in a circuit due to number of sources is given by the sum of individual sources acting alone. ii) The property of homogeneity says that if all the sources are multiplied by a constant then the response is also multiplied by the same constant

26. What are ideal elements? The ideal elements are resistors which oppose the flow of current; the inductor opposes to change in current. Capacitor offers only opposition to change in voltage.


27. State dot rule for coupled coils. a. It states that in coupled coils current entering at the dotted terminal of one coil induce an emf in second coil which is +ve at dotted terminal of second coil. b. Current entering at the un dotted terminal of one coil induce an emf in second coil which is +ve at un dotted terminal of second coil.

UNIT-4

TRANSIENT RESPONSE FOR DC CIRCUITS

1. What is transient? The state of the circuit from the instant of switching to attainment of steady state is called transient state.

2. Why transients occurs in electric circuits. The inductance will not allow sudden change in current and the capacitance will not allow sudden change in voltage. Hence in inductive and capacitive circuits transient occurs during switching operation.

3. What is free and forced response? The response of the circuit due to stored energy alone is called free response. The response of a circuit due to an external source is called forced response.

4. What is complementary function? The part of the response which becomes zeroes t tends to infinite is called complementary function. 5. What is particular solution? The part of the solution which attains a steady value as t tents to infinity is called particular solution.

6. Define time constant of RL circuit. It is defined as the time taken by the current through the inductance to reach steady value if initial rate of rise is maintained. 7. Define time constant of RC circuit. The time constant RC circuit is defined as the time taken by the voltage across the capacitance to reach steady value if initial rate of rise is maintained.OrThe time constant for the RC circuit is the time during which the current falls to 36.8% of initial current.

8. Define a time constant of a R-L circuit.The time constant of R-L series circuit is defined as the period during in which the current rises to 63.22% of its final value. 9. What is damping ratio. The ratio of resistance of the circuit and resistance for critical damping is called damping ratio.


10. What is critical damping. It is the condition of the circuit at which the oscillations in the response are just eliminated. This is possible by increasing the value of resistance in the circuit.

11. What is natural and damped frequency? a. The response of a circuit is completely oscillatory with a frequency in the absence of resistance and this frequency is called natural frequency. b. The response of under damped circuit is oscillatory with a frequency and these oscillations are damped as t tends to infinity. The frequency of response is called damped frequency.

12. What is meant by source transformation? The voltage source can be converted in to equivalent practical current source and vice versa with same terminal behavior. 13. What is the steady state value?A circuit consisting of constant source is said to be in steady state if the voltages and currents do not change with time.

14. What is cutoff frequency? The frequency that separates the pass and attenuation bands

15. What is driving point impedance? It is defined as the ratio of transform voltage to current at the same port. 16. What is Transfer impedance? It is defined as the ratio of transform voltage at one port to the current transform at the other port.

UNIT-5

ANALYSING THREE PHASE CIRCUITS

1. What is balanced voltage? In poly phase system when the magnitude of phase voltages are equal and the phase difference between consecutive phasor are equal then the voltages are called balanced voltages.

2. What is balanced impedance? When the impedances of all the phases of a three-phase load are equal then the impedances are called balanced impedance.

3. What is phase sequence? In a set of rotating phasors, the order of reaching reference point is called phase sequence.

4. Write the relation between the line and phase value of voltage and current in a balanced star connected load. In star connected load the line current and phase current are same. In balanced star connected system the magnitude of line is √3 times the phase voltage and it leads the phase voltage by 30degree


.5. Write the relation between the line and phase voltage of voltage current in a balanced delta connected load. In a delta connected system the line voltage and phase voltage are same. In balanced delta connected load the magnitude of line current is√3 times the phase current and it lags the phase current by 30 degree.

6. What is neutral shift voltage? In three wire star connected load, the load neutral is not connected to source neutral. Therefore when the load is unbalanced the load neutral will not be at zero potential. The voltage of load neutral with respect to source neutral is called neutral shift voltage.

7. Write the relation between the power factor and wattmeter readings in two-wattmeter method of power measurement. a. When the wattmeter readings are equal the power factor is unity. b. When one of the wattmeter reading is zero the power factor is 0.5. c. When both the readings are +ve the pf will be greater than 0.5.

8. What are ideal elements? The ideal elements are resistors which oppose the flow of current; the inductor opposes to change in current. Capacitor offers only opposition to change in voltage.

9. What are the advantages of three phase system?1.The generation and transmission of electrical power are more efficient.2.The power transmitted in a three phase circuit is constant rather than pulsating as in a single phase circuit.3.Three phase motors start and run much better than single phase motors.. 10. Write the expression for total power in a 3 phase system.Ptotal = 1.732 VL X IL COSϴPtotal = 3 Vph X Iph

11. The wattmeters in line A and line B of a 120 volts ,RYB System read 1500 watts and 500 watts respectively.find cosФ(p.f) of the balanced delta connected load

W1 = 1500 watts. W2= 500watts Total power = 1500+500 = 2000 watts.

TanФ = 1.732 ( wi-w2) / (w1+w2)

TanФ = 0.866, Ф = 40.89

p.f = cos(40.89)

12. A balanced 3 phase star connected load of 150 kw takes a leading current of 100 amps with line voltageof 1100v,50 hertz.find the p.f?P= 150 kw ,, I = 100 Amps , V= 1100volt Power = 1.732 line voltage x line current x power factor p.f = 0.7873

13. What is Band width and Selectivity?


The frequency band within the limits of lower and upper half frequency is called Bandwidth. B.W = f2-f1 Selectivity is the ratio of fr to the B.W Selectivity = fr / (f2-f1)

14. A coil having an inductance of 100 millihenry is magnetically coupled to another coil having an inductance of 900 millihenry.The mutual inductance between the coil is 135 milli henry.Find the equivalent inductance if the two coils are connected in series aiding and opposing.Series aiding = L1+L2+2M= 100 +900 +2(135) = 1270 milli henry

Series Opposing = L1+L2-2M= 100+900-2(135) = 730 milli henry

15. What is driving point impedance? It is defined as the ratio of transform voltage to current at the same port.

16. What is Transfer impedance? It is defined as the ratio of transform voltage at one port to the current transform at the other port.

17. State compensation theorem. a. Let I be the current through an impedance Z in a branch of circuit. b. It states that the change in current due to change in impedance in a branch will be produced by a compensation voltage source in the same branch with polarity opposing the original current.

18. State Millman’s theorem. It states that if n number of voltage sources with internal impedance are in parallel then they can be combined to give a voltage source with an equivalent emf and internal impedance. 19. State Tellegen’s theorem. It states that the summation of all the product of branch voltage and its current of a circuit is zero.

PART B – QUESTION

1. Explain different types of powers and draw the power triangle? 2. Explain over damped, under damped and critically damped conditions for a series RLC circuit? 3. Derive an expression for the DC transient for RC circuit and also for voltage and power across each element? 4. What is meant by the term time constant? 5. Write an expression for calculating real, reactive and apparent powe in an AC circuit? 6. State superposition theorem and reciprocity theorems with examples? 7. State thevenins theorem and nortens theorems with examples? 8. Explain Krichoff’s Voltage and Current laws with examples? 9. Find the equivalent delta for a star system? 10. Tabulate the analogy between magnetic and electric circuit?


11. Explain in detail about the Mutual inductance self-inductance and couling and coefficient of coupling? 12. Which system draws less current if one system is star connected and the other is delta connected when they have equal resistance? And find the power loss in the system? 13. What do the Fourier coefficients represent? And explain in detail. 14 Give the Laplace transform equation for a step, ramp, parabolic and impulse functions? 15. Derive an expression for current i(f) for series R-L Circuit when the step input is applied? 16. Derive the response equation for a series RLC circuit/ 17. Derive the response equation for a parallel RLC circuit? 18. Derive the relation between coefficient of coupling and the self-inductance and mutual inductance? 19 Explain in detail about the time constant in RL circuit and explain about the dual and duality of a circuit 20. A series RLC circuit with = 10 R , L = 10 mH and C = 1 µf has anapplied voltage of 200 V at resonance frequency. Calculate the resonantfrequency, the current in the circuit and the voltage across the elementsat resonance. Find also the quality factor and band width for the circuit.21. Two wattmeters are connected to measure the power in a 3Phase , 3 wirebalanced load. Determine the total power and power factor if thetwo wattmeters read (1) 1000 w each, both positive (2) 1000 w each,of opposite sign.

22. In the circuit shown in figure below , find the different node voltages andthe currents 2 1, I I and 3 I .

(a) In the circuit shown in figure below, find the different mesh currents,power delivered by each source and the current through RL.

23. (a) In the circuit shown in figure below. find(i) the equivalent resistance between P and Q. (ii) the total current from the 240V source. (iii) The current through the 18 resistor.

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24. Derive an expression for total inductance of two coupled coils connected in 1. Series aiding mode 2. Series opposing mode.

25. Calculate the total power input and readings of the two wattmeter connected to measure power in 3phase balanced load .If the reactive power input is 15KVAR and the p.f is 0.8 .Also compute the load KVA.

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circuit theory 2-marks

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