BHARATHIDASAN ENGINEERING COLLEGE QUESTION BANK BEC/FIRST YEAR/EE6201-CIRCUIT engineering college question bank department of electronics and communication engineering year/sem : i / ii name of the subject: ee6201 circuit theory
BHARATHIDASAN ENGINEERING COLLEGE QUESTION BANK DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING YEAR/SEM : I / II NAME OF THE SUBJECT: EE6201 CIRCUIT THEORY NAME OF THE FACULTY: A.R. DINESH KUMAR SYLLABUS ( X ) * Ohms Law - Kirchoffs laws - DC and AC Circuits - Resistors in Series and Parallel Circuits ( Y ) * Mesh Current and Node Voltage Method of analysis for D.C and A.C. Circuits Phasor Diagram Power, Power Factor and Energy PART A IX1 Find the equivalent conductance of the circuit shown below ( Nov/Dec 2012) ( April/May 2013) (April/May 2013) IX2 State the Limitation of Ohms law. IX3 Determine current in the circuit of fig (April/May 2014) (April/May 2014) IX6 IX7 IX8 IX4 Determine the current through 20 resister in the circuit of fig ( April/May 2014) IX5 Find the equivalent resistance of the circuit shown in fig ( May/June 2014) Define RMS voltage ( May/June 2014) An electrical appliance consumes 1.2kwh in 30 mins at 120V.what is the current drawn by the appliance? Nov/Dec 2014) ( Calculate the equivalent resistance between the terminals a & b in fig ( Nov/Dec 2014) (April/May 2015) IX9 Obtain current in the each branch of the network shown below using (April/May2015) kirchhoffs current law IX10 State Kirchoffs Voltage law (April/May2015) IX11 (Nov/Dec 2014) Define ohms law (April/May 2016) IY9 (ii) ( Nov/Dec 2014) IX12 Write briefly about resistance in a circuit ( April/May 2015) IY13 Define mesh analysis of a circuit ( Nov/Dec 2012) IY14 Distinguish between mesh & loop of an electric circuit. ( April/May 2013) IY15 Write the expression for mesh current equations in matrix form ( Nov/Dec 2014) IY16 what are three types of power used in A.C circuit? ( April/May2015) PART B Find the equivalent resistance between the terminals a & 4 b for the network shown in fig IY7 ( i) Determine the current through each resistor in the circuit 6 May/June ( 2014) shown fig (April/May 2017) IXI (ii) State and explain kirchoffs Laws. 6 (April/May2013, Nov/Dec 2014) IY4 (i) Three loads A, B and C are connected in parallel to a 240 V source. Load A takes 9.6 KW, Load B takes 60 A and Load C has a resistance of 4.8 . Calculate (i) (1) and (2) the total current (3) the total power, and (4) equivalent resistance. 6 (April/May 2013) IY6 (i) Find the current I and voltage across 30 of the circuit 8 (May/June 2014) shown in fig IXI i) ( Determine the current I L in the circuit shown in figure below: 8 Nov/Dec 2012) ( IY1 ( i) For the circuit shown in figure below, determine the total 8 ( Nov/Dec 2012) current I T , phase angle and power factor. IY1 (ii) In the circuit given below ,obtain the load current 8 Nov/Dec 2014) ( (April/May 2018) IY6 (ii) Determine the current in all the resistors of the circuit 8 (May/June 2014) shown in fig IY7 (ii) When a dc voltage is applied to a capacitor,voltage across 10 (May/June 2014) its terminals is found to build up in accordance with IY8 ( i) Derive the expressions for resistors in parallel & series 8 Nov/Dec 2014) ( IY8 ii) ( Two 50 resistors are connected in series.when a resistor R is connected across one of them,the total circuit resistance is 60 .calculate the value of R.if the supply voltage across the above circuit is 60V,find the current passing through individual resistance. 8 ( Nov/Dec 2014) Y3 Using mesh analysis, determine the current through 1 10 resistor in the given circuit. IY4 ( ii) By applying nodal analysis for the circuit shown in Fig, 10 determine the power output of the source and the power in each resistor of the circuit. (April/May 2019) vc=50(1-e-100t).After 0.01S the current flow is equal to 2mA. (1) Find the value of capacitance is farad. (2) How much energy stored in the electric field? IY5 IY9 i) ( Using node analysis,find the node voltages &b the currents through all the resistors for the circuit shown in fig 12 ( Nov/Dec 2014) IY2 For the circuit shown in the figure, Determine the value of 16 ( Nov/Dec 2012) V 2 such that the current through (3+j4) Impedance is zero. ( i) Determine the currents in all branches 16 ( ) ii Calculate the power & power factor of the source iii ) ( Show that po wer delivered by the source is equal to power consumed by 2 resistor (April/May 2020) IY10 For the circuit shown in fig,find the(i)currents in different 16 ( Nov/Dec 2014) branches,(ii) current supplied by the battery,(iii) potential difference between terminals A & B IY11 Determine the current supplied by each battery in the 16 (April/May 2015) circuit shown below using mesh analysis IY12 Use nodal voltage method to find the voltages of nodes m 16 ( April/May 2015) & n and curr ents through j2 & - j2 reactance in the network of fig Use branch currents in the network shown below to find 16 the current supplied by the 60V source.Solve the circuit by the mesh current method. (April/May 2021) IY13 IY14 Solve the network given below by the node voltage method 16 ( April/May 2015) UNIT II SYLLABUS (X) * Network reduction: voltage and current division, source transformation - star delta Conversion. (Y) * Thevenins and Norton & Theorem Superposition Theorem Maximum power transfer theorem Reciprocity Theorem. IIX6 How to change the (a) current source into voltage source (b) voltage source into current source? (Nov09) PART A IIX1 State the voltage division principle for two resistor in series and the current division principle for two resistor In parallel. ( May13) IIX2 Find the equivalent current source for a voltage source of 100V with series resistance of 2 . ( May12) IIX3 Find the equivalent current source for the circuit shown in fig ( May10) IIX4 Write the objective of star delta transformation. ( Nov13) IIX5 For the network shown in the following fig, convert the voltage ( Nov10) source into current source IIX7 IIX8 IIX9 IIX10 IIX11 IIX12 IIY13 State Maximum Power transfer theorem. (May13,May10) IIY14 State Reciprocity theorem. (May12,Nov13) IIY15 State Thevenins Theorem. (May11) With example explain the transformation of three voltage source is in series with three resistance combination? ( Nov09) Write the formula for star to delta transformation. ( May09) Write the formula for delta to star transformation. ( May09) Draw the equivalent current source transformation circuit for the following circuit. ( Nov/Dec 2014) Give a delta circuit having resistors, write the required expressions to transform the circuit to a star circuit. ( Nov12) Transform the circuit shown below, from delta to star. ( May11) IIY16 In the circuit shown below, find the value of the load impedance ZL for maximum Power Transfer to the load. (Nov12) IIY17 IIY18 IIY19 IIY20 IIY21 IIY22 IIY23 State Super Position Theorem ( May10) State Nortons Theorem ( May10) Draw the equivalent circuit for Nortons theorem ( Nov09) Which theorem is used to find the maximum power for a Linear/nonlinear network? ( Nov09) Write the formula for finding the Thevenins resistance ( May09) Compare Thevenins theorem and Nortons theorem ( Nov09) What is the current formula for Maximum power transfer theorem? ( Nov10) Which theorem is applicable for linear / bilateral networks? ( Nov11) State reciprocity theorem. ( Nov/Dec 2014) Draw the equivalent circuit for Thevenins theorem ( Nov10) PART B IIY12 State and explain superposition theorem. 6 IIY24 IIY25 IIY26 IIX1 (i) Use the technique of delta-star conversion to find the 8 (May11) equivalent resistance between terminals AB of the circuit shown below. IIX1 (ii) Explain the source transformation technique. 8 (May13) IIX2 (May11) ( i) Use source transformation to find I0 in the circuit shown 8 below. IIX2 (ii) Using source transformation, replace the current source in 8 ( Nov12) the circuit shown below by a voltage source and find the current delivered by the 50V voltage source. IIX5 i) ( Explain the conversion from a star circuit to delta circuit. 8 ( Nov/Dec 2014) IIX5 ii) ( In the circuit given below, obtain the equivalent resistance at AD. 8 ( Nov/Dec 2014) IIY6 i) ( Use the superposition theorem to find the current through 8 May13) ( 4 resistor in the circuit shown in fig. IIY8 (ii) IIY9 (i) Determine the voltage across 20 resistance in the circuit 8 (May11) shown below, using superposition theorem. IIY6 (ii) Calculate the equivalent resistance Rab when all the 8 Nov12) ( resistance values are equal to 1 for the circuit shown below. IIY7 (i) Derive expression for star connected resistances in terms of 8 ( May13) delta connected resistances. IIY7 (ii) Find the current trough branch a - b of the network shown in 8 fig. using Thevenins theorem. IIY8 (i) Calculate the current through 2 resistor in the circuit 8 May12) ( shown in fig, using superposition theorem. Calculate the current through 2 resistor in the circuit 8 shown in fig using thevenins theorem. IIY12 Find the current through 10 resistor in fig, using 10 (Nov13) Thevenins Theorem. Q. IIX3 In the circuit shown below, find 16 ( May10) ( i) The equivalent resistance between P and ( ii ) The total current from 240V source. ( iii ) The current through 18 resistor. IIX4 Using star - delta transformations, in the following wheat 16 ( Nov13) stone bridge circuit of fig, find (i) the equivalent resistance between P and Q, (ii) the total current (iii) The current through 18 resistor. UNIT III SYLLABUS (X) * Series and Parallel resonance Their frequency response Quality factor & Bandwidth (Y) * Self and Mutual inductance Coefficient of coupling Tuned circuits Single tuned circuits. PART A IIIX1 Define band width of a resonant circuit. (May13,May09) (Nov/Dec 2014) IIIX2 Define Resonant network. (May12) IIIX3 When do you say that a given AC circuit is at resonant? (May11) IIIX4 In a series RLC circuit, If the value of L and C are 100Uh and o.1Uf respectively. Find the resonance frequency in HZ (May10) IIIX5 Define quality factor of a coil (May09) IIIX6 Write the significance of quality factor. (Nov13) IIIX7 A series resonant circuit has a bandwidth of 20KHz and a (Nov12) quality factor of 40. The resistor value is 10 Kohm. Find the value of this circuit IIIX8 Write the condition of resonance (Nov11) IIIX9 Draw the series resonance, parallel resonance circuits and phasor diagram. (Nov11) IIIX10 Compare series and parallel resonance circuits. (May11) IIIX11 Determine the value of capacitive reactance and impedance at resonance. When R = 10ohm, C =25F and L =10Mh (Nov10) IIIX12 Mention the relationship between Q-factor and bandwidth (May10) IIIX13 What is resonance frequency and Bandwidth of a series RLC circuit in which R=5ohm, L=40Mh, C=1F? (Nov09) IIIX14 Draw the frequency response of R-L circuit and explain. (May11) IIIX15 What do you understand by damped frequency? (Nov10) IIIX16 In a parallel RL circuit R=3ohm and XL =4ohm.What is the ( Nov12) ( Nov10) ( Nov10) ( May11) value of admittance? IIIY17 Give the applications of tuned circuits. (May13) IIIY18 State Dot rule for coupled circuits IIIY19 Two inductively coupled coils have self inductances L1=50 mH and L2=200 mH. If the coefficient of coupling is 0.5, Compare the value of mutual inductance between the coils. (May11) IIIY20 Write the empirical formula for coefficient of coupling in coils. (Nov13) IIIY21 Define Mutual inductance. IIIY22 Define coefficient of coupling? IIIY23 What is the maximum possible mutual inductance of two Inductively coupled coils with self-inductance L1=25mH and L2=100mH? IIIY24 Two inductively coupled coils have self-inductance L1=45 mH and L2=150 mH. If the co-efficient of coupling is 0.5, (i) find the value of mutual inductance between the coils and (ii) what is the maximum possible mutual inductance? PART B IIIX6 (ii) State the concept of bandwidth of a series RLC circuit. 2 IIIX6 (iii) A series RLC circuit consists of 50 ohm resistance, 0.2 4 H inductance and 10 uF capacitance with the applied voltage of 20 V. Determine the resonant frequency, Q factor, the lower and upper frequency limits and the bandwidth of the circuit. IIIX1 (i) Derive the resonance frequency f,for the circuit shown 8 (May13) in fig IIIY10 (i) In the coupled circuit shown below. Find the voltage across 5 8 (May11) ohm resistor. IIIX1 ( ii) A series circuit with R=10 ohm, L=0.1H and C=50uF has an applied voltage V=50 V with a variable frequency. Find ( i ) the resonant frequency (ii) the value of frequency at which maximum voltage occurs across inductor (iii) the value of frequency at which maximum voltage occurs across capacitor (iv) the quality factor of the coil. 8 IIIX2 ( i) The signal voltage in the circuit shown in fig is e(t)=0.01 sin ( 2 45510 3 ) V.What should be the value of C in order that the circuit would resonant at this signal frequency? At this condition, find the values of I,Vc,Q and bandwith of the circuit. 8 ( May12) IIIX2 ii) ( RL+20)ohm and ( (20 - j10) ohm are connected in parallel . Determine the value of RL for resonanace. 8 IIIX3 ( i) For the tank circuit shown below, find the resonance frequency fr. 8 May11) ( IIIX3 ii) ( Determine the quality factor of the coil for the series circuit consisting of R=10 ohm, L=0.1 H and C=10 uF. Derive the formula used. 8 IIIY14 (ii) Two coupled coils have self inductances of L1=100 mH and L2=400 mH. The coupling coefficient is 0.8. Find M. If N1 is 1000 turns, what is the value of N2? If a current i1=2 sin(500t) A through the coil 1, find the flux and the mutually induced voltage V2m. 8 IIIY15 (i) Co-efficient of coupling. 8 (Nov/Dec 2014) IIIY15 (ii) Tuned circuit 8 IIIY10 ( ii) Derive the expressions for maximum output voltage and maximum amplification of a single tuned circuit. 8 ( May11, Nov13) IIIY11 i) ( Derive the expression for coefficient of coupling in terms of mutual and self inductances of the coils. 8 13) ( May IIIY11 ( ii) Consider the single tuned circuit shown in fig. determine ( a) the resonant frequency (b) the output voltage at resonance (c) the maximum output voltage. Assume RS>> wrL1 and K=0.9. 8 ( May13, May12) IIIY14 ( i) Obtain a conductively coupled equivalent circuit for the 8 ( Nov12) magnetically coupled circuit shown below. IIIX6 (i) Derive the resonance frequency fr for the circuit below. 10 (Nov12) UNIT IV SYLLABUS (X) * Transient response of RL, RC and RLC Circuits using Laplace transform for DC input IIIX7 A RLC series circuit has R=60 ohm,L=160 mH and C=160 uF. Find the resonant frequency under resonant condition obtain the current, power and the voltage drop across the various elements if the applied voltage is 300V. 16 Nov13) ( IIIX8 For a series RLC circuit 16 Nov/Dec 2014) ( ( i) Derive the condition for resonance ( ii) Explain the frequency response and ( iii) Obtain the quality factor and bandwidth IIIY9 Derive the relationship between self - inductance , mutual inductance and coefficient of coupling. 16 May12, ( May10) IIIY12 In the circuit shown in fig, find the value of I1 and I2 and also the real power supplied by each source. 16 ( May10) IIIY13 Explain the single tuned and double tuned circuit. 16 ( May09) (Y) * Transient response of RL, RC and RLC Circuits using Laplace transform for A.C. with sinusoidal input Characterization of two port networks in terms of Z,Yand h parameters. PART A IVX1 What is meant by transient time? (Nov13) IVX2 Compare steady state and transient state (Nov11) IVX3 A series RL circuit with R=100 ohm and L=20 H has a dc Voltage of 200V applied through a switch at t=0. Assuming (May10) the intial current through the inductor t=0 is zero, find the current at t=0.5 sec. IVX4 Draw the DC response of R-L circuit and the response curve. (May11) IVX5 Draw the DC response of R-C circuit and the response curve (May11) IVX6 Draw the DC response of R-L C circuit and the response (Nov10) curve IVX7 Write the purpose of Laplace transformation in the circuit Analysis. (Nov13) IVX8 Write any two advantages of laplace transformation. (Nov/Dec 2014) IVX9 Define damping ratio? (May11) IVX10 Find the time constant of RL circuit having R=10 ohm and L=0.1 mH. (May13) IVX11 Define transient,forced response (Nov11) IVX12 What is the condition to be present in a series RLC circuit to (May10,Nov12) make the circuit critically damped? IVX13 A RLC series circuit has R=10 ohm, L=2 H. What value of capacitance will make the circuit critically damped? (May13) IVX14 Define the term Time Constant of a circuit, in general. (May11) IVY15 Write the expression for the laplace transformation of sine function, (sin t). (Nov/Dec 2014) IVY16 Sketch the current given by i(t)= 5 4 e-20t. (May11) case in the two cases. IVY21 Calculate the impedance. IVY22 Circuit. IVY23 IVY24 conditions PART B IVX1 Derive the transient response of series RLC (May12) circuit, with DC input, using Laplace transform (a) Derive the necessary differential equation and solve. 4 (b) Discuss the cases of over damping, critical and 4 under damping. IVY17 Draw the sinusoidal response of R-L -C circuit and write the differential equation (May10) IVY18 Draw the sinusoidal response of R-C circuit and write the Differential equation. (May10) IVY19 Draw the sinusoidal response of R-L circuit and write the Differential equation. (Nov10) IVY20 Consider two cases RC parallel circuit shown below. First When DC voltage is applied and second case when AC voltage is applied. Compare how the capacitor gets charged ( May12) A coil having a resistance of 10 Kohm and inductance of 50 mH is connected to a 10 V, 10 KHz power supply. ( May11) Sketch the transient current i(t) vs t graph for a series RL ( May12) Determine Laplace transform for the unit step function u(t). ( Nov12) Write the steps to be involved in the determination of initial ( Nov12) (c ) Express the solution in terms of undamped 4 natural frequency, damped natural frequency and damping factor. (d) Sketch the transient response curve for the three cases. 4 IVX2 (i) Using Laplace transform, obtain the expression for i1 and i2 8 (May11) in the circuit shown below, when dc voltage source is applied suddenly. Assume that the initial energy stored in the circuit is zero. (ii) In the circuit shown in fig,find the expression for the 8 transient current ,the initial current is as in fig Derive the transient response of a series RL circuit with DC 8 ( Nov12) input. Sketch the variation of current and of the voltage across the Solve for I and V as functions of time in the circuit shown 8 Below , when the switch is closed at time t=0. IVX5 A series RL circuit with R=30 & L=15H has a constant 16 May/June 14 Voltage V=60v applied at t=0 as shown in fig. Determine the current I, the voltage across resistor and the voltage across the inductor . IVX6 The circuit shown in fig consists of R,L & C in series with 16 May/June 14 V DC when the switch is closed at t=0.find the current 100 transient. IVX4 (i) inductor. (ii) IVX3 In the circuit shown in fig, the switch S is closed at time t=0 16 (Nov13, May10) in position 1 and changed over to position 2 after 1msec. Find the time at which the current is zero and reversing its direction. Assume that the changeover of switch from position 1 to 2 takes place in zero time. IVX7 Derive the step response of RL and RC circuits. Compare 16 (May13) their performances. IVY8 Derive an expression for the current response of RLC series circuit with sinusoidal excitation. Assume that the circuit is working in critical. IVY9 Derive an expression for the current response of RLC series circuit with sinusoidal excitation. From the results, discuss the nature of transient and steady state responses. Comment on the phase angle involved. IVY10 In the circuit shown in fig, find the expression for current if 16 (Nov13,May10) the switch is closed at t=0 and the value of current at t=1 msec. Assume initial charge on the capacitor is zero. IVY11 Derive the expression for the complete solution of the current 16 (Nov12) response of RC series circuit with an excitation of Vcos(wt+fi ). Briefly explain the significances of phase angle in the solution. IVY12 A series RL circuit with R=100 ohms and L=1 H has a 16 (Nov/Dec 2014) sinusoidal voltage source 200sin (500t+) applied at a time when =0. (i) Find the expression for the current. (ii) at what value of angle must the switch be closed so that the current directly enters the steady state. (16) IVY13 Explain in detail with neat illustrations the high pass & low pass networks and derive the necessary network parameters 16 April/May 2015 IVY14 Explain the characterization of two port networks in terms of Z,Y & h parameters 16 April/May 2015 UNIT V SYLLABUS (X) * Three 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 (Y) * Power and Power factor measurements in three phase circuits. 16 ( May13) 16 3,50Hz supply. Calculate phase voltage. Ia=10 - VX8 VX9 What is the difference between balanced and unbalanced circuits? Explain how to solve unbalanced neutral isolated three phase load connected to a balanced supply? 120 A, Ib=5 150 A. (Nov11) What is the line current (May11) Ic? VX10 What is meant by positive, negative, zero sequence VX6 VX7 Write the current relations in star and delta connections of a three phase circuit. Three inductive coils each having resistance of 16 and (Nov13) reactance of j12 are connected in star across a 400V, (Nov12) PART A VX1 What is a phase sequence of a 3 - phase system? May13) ( VX2 A delta connected load has (30 - j40) impedance per phase. Determine the phase current if it is connected to a 415V, 3, and 50Hz supply. ( May13) VX3 What are the advantages of 3 - phase systems? May13,Nov13) ( VX4 A 3, 440V supply is given to a balance star connected load of impedance (6 - j8) in each branch. Find the magnitude of the line current. ( May12) VX5 In the circuit shown in fig, find the rms value of line current and phase voltage. May10) ( VY20 Define power factor. (May12) VY21 In a 3 balanced delta system, the voltage across R and Y is 400 VY29 Write the distortion power factor equation of 3 circuits April/May 15 VY30 Write the effect of power factor in energy consumption billing May/June 14 PART B VX2 (i) What are the advantages of 3-phase systems? 6 (May13,Nov13) VX1 (i) Prove that the total instantaneous power in a balanced three 8 (May13) phase system is constant and is equal to the average power whether the load is star or delta connected. (ii) An unbalanced star connected load has balanced voltages of 8 100V and RBY phase sequence. Calculate the line currents and the neutral current. Take ZA=15Q, ZB=(10+jfi)Q, Zc=(6-j8)Q. May10) ( VY24 A 3 Motor can be regarded as a balanced star load. A 3 motor drawn 5.6 KW when the line voltage is 220V and the line current is 18.2A. Determine the PF of the motor. ( Nov12) VY25 In the measurement of three phase power using two wattmeter method , when both the wattmeter read same values, what is the value of power factor of the load? Nov11) ( VY26 A balanced star connected load of (3 - j4) impendance is connected to 400 V,3 supply. What is the real power consumed? ( May09) VY27 A symmetrical three phase, 400 V system supplies a balanced mesh connected load. The current in each branch circuit is 20A and the phase angle is 40 degree lag. Fine (a) the line current ( b) the total power. ( Nov09) VY28 Write the expression for three phase total power. ( Nov/Dec 2014) VX3 (i) An unbalanced star connected load is supplied from a 8 (May10) 3 440V, symmentrical system. Determine the line currents and the power input to the circuit shown in fig. Assume RYB sequence. Take phase voltage VRB as reference in the supply VY6 (i) If W1 and W2 are the readings of the 2 wattmeters which 8 (May12) measures power in the three phase balanced system and if W1/W2=a, shows that the power factor is cos()=(a+1)/Sqrt(a^2-a+1). (ii) Obtain the readings of two wattmeters connected to a 3 3 8 wire 120V system feeding a balanced delta connected load impedance of 12 VY7 (i) 2 wattmeters are connected to measure the power in a 3 3 8 (May10) wire balanced load. Determine the total power and power factor if the 2 wattmeters reading (a) 1000W each both Positive. (b) 1000W each of opposite sign. VY7 ( ii) For the circuit shown below, calculate the line current, the 8 ( Nov12) power and the PF. The values of R, L and C in each phase are 10 , 1H and 100uF respectively. VY9 ( i) A 3 400 Volts supply is given to a balanced star connected load of impedance 8+j6 s in each branch. Find the line current, power factor and total power. 8 Nov/Dec 2014) ( VY9 ii) ( impedances Z 1=( 3 17.32+j10) , Z2=(20+j34.64) and Z 3=(0 - j10) s are delta connected to a 400V, three Phase system. Determine the phase currents, line currents and total power consumed by the load. 8 VX2 ( ii) Determine the line currents for the unbalanced delta connected load shown below, phase sequence is RYB. 10 ( May13,Nov13) VX4 Explain the behaviour of unbalanced loads in 3phase system. 16 (Nov13) VY8 Explain power and power factor measurements in three phase 16 (Nov/Dec 2014) circuits by two wattmeter method.