EE6201-CT-U1-5-QB

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Anna University – ChennaiDepartment of Electrical and Electronics Engineering

EE 6201 – CIRCUIT THEORY

COMMON FOR EEE/ EIE/ECE

UNIT I BASIC CIRCUITS ANALYSIS

Part – A- Two marks questions

1. State Ohm’s law and list its limitations.

2. What is meant by active and passive elements?

3. What is meant by Unilateral and bi-lateral element?4. What is a phasor?

5. Define power factor.

6. Define RMS value.7. Define an ideal voltage source.

8. Define an ideal current source.

9. Name the four different types of dependent sources in electric circuits.10. Applications of series and parallel combination.

11. State two salient points of a series combination of resistance.

12. State two salient points of a parallel combination of resistance.13. What is meant by linear and nonlinear elements?

14. Define Average value.

15. Write the expression for impedance in the RLC series circuit.

Part –

B 16 marks questions

1. Find the current through each branch by network reduction technique.

2. Calculate a) the equivalent resistances across the terminals of the supply, b) total current

supplied by the source and c) power delivered to 16 ohm resistor in the circuit shown in figure.

3. In the circuit shown, determine the current through the 2 ohm resistor and the total current

delivered by the battery. Use Kirchhoff’s laws.

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4. In the network shown below, find the current delivered by the battery.

5. Determine the mesh currents I1 and I2 for the given circuit shown below

6. Determine the value of V2 such that the current through the impedance (2+j3) ohm is zero.

7. Use Nodal Voltage method and find the power dissipated in the 10 Ω resistance on the circuit

shown in th fig

8. Given the nodes 1 and 2 in network of figure,

Find the ratio of voltage V1 / V2

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UNIT II NETWORK REDUCTION AND NETWORK THEOREMS FOR DC AND Part –

A- Two marks questions

1. Explain how voltage source with a source resistance can be converted into an equivalent

current source.

2. Find The Equivalent Current Source for a Voltage Source Of 10v In Series With A 60ohmResistance.

3. Find the equivalent voltage source for a current source of 15A when connected in parallel

with 5 ohm resistance.4. Given that the resistors Ra, Rb and Rc are connected electrically in star. Write the equations

for resistors in equivalent delta.

5. Three equal resistors each of R ohms are connected in star. Find the value of resistors in the

equivalent delta.6. Three resistors Rab, Rbc and Rca are connected in delta. Write the expression for resistors in

equivalent star.

7. Three resistors, each of value R ohms are connected in delta. Find the value of resistors in itsequivalent star.

8. How will you obtain the Norton’s equivalent circuit from Thevenin’s equivalent circuit?

9. State Superposition theorem.

10. State Thevenin’s theorem.11. State Norton’s theorem.

12. State Maximum power transfer theorem.

13. State reciprocity theorem.14. Write some applications of Maximum power transfer theorem.

15. A voltage source has internal impedance (4+j5) ohm. Find the load impedance for Maximum

power transfer.

Part – B 16 marks questions

1. Derive expressions for star connected arms in terms of delta connected arms and delta connected

arms in terms of star connected arms. (16 marks)

2. Determine Thevenin’s equivalent across the terminals AB for the circuit shown in figure below.(16 marks)

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3. a) Find the current through branch a- b network using Thevenin’s theorem. (8

marks)

3. b) Find the current in each resistor using superposition principle of figure. (8 marks)

4. For the circuit shown, use superposition theorem to compute current I. (16 marks)

5. Using superposition theorem calculate current through (2+j3) ohm impedance branch of the

circuit shown. (16 marks)

6. a) Find the value of RL so that maximum power is delivered to the load resistance shown in

figure. (8 marks)

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6. b) State and explain reciprocity theorem. (8 marks)

7. a) State and explain maximum power transfer theorem for variable pure resistive load. (8

marks) b) Using Norton’s theorem, find current through 6 ohm resistance shown in figure. (8

marks)

8. Determine the maximum power delivered to the load in the circuit. (16 marks)

UNIT III RESONANCE AND COUPLED CIRCUITSPart – A- Two marks questions

1. Define quality factor.

2. What are half power frequencies?3. What is DOT convention?

4. Write the characteristics of series resonance.

5. What is anti resonance?6. Write the characteristics of parallel resonance.

7. What is Band width and Selectivity?

8. Mention the Properties of a series RLC circuit.

9. Mention the Properties of a parallel RLC circuit.10. What is resonance?

11. What are coupled circuits and coupled coils?

12. State dot rule for coupled coils.` ``` 13. Define self-inductance.

14. Define mutual inductance.

15. Define coefficient of coupling.

Part –

B 16 marks questions1. Explain and derive bandwidth and half power frequencies for a series RLC Ciruit as a function

of resonant frequency. (16 Marks)

2. A series RLC circuit has the following parameter values: R = 10 ohms; L=1 H and C = 1 µF.

a) Compute the resonant frequency in radians/sec. b) Calculate the quality factor of the circuit.

c) What is the value of the bandwidth?

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d) Calculate the lower and upper half power frequency points of the bandwidth in

radians/sec. (16 Marks)

3. A constant voltage at a frequency of 1 MHz is applied to an inductor in series with a variablecapacitor. When the capaccittorr is set to 500pF, the current has the maximum value, while it is

reduced to one half when the capacitance is 600pF. Find (i) the resistance (ii) the inductance (iii)

the Q factor of the inductor. (16 Marks)4. a) A current source is applied to a parallel combination of R, L and C. where R = 10 ohms, L =

1 H and C= 1 µF.

a. Compute the resonant frequency b. Find the quality factor.

c. Calculate the value of the bandwidth.

d. Compute the lower and upper half frequency points of the bandwidth. (8 Marks)

b) For the parallel network shown in figure, determine the value of R for resonance. (8 Marks)

5. a) A coil of 20 Ω resistance has an inductance of 0.2 H and is connected in parallel with a

condenser of 100 µF capacitance. Calculate the frequency at which the circuit will act as anon – inductive resistance of R ohms. Find also the value of R.

(8 Marks)

b) Determine the value of the capacitance C in order that the circuit in the figure is resonantat 6366 Hz.

(8Marks)

6. The number of turns in a coil is 250. When a current of 2A flows in this coil, the flux in thecoil is 0.3 mweb, when this current is reduced to zero in 2 msec, the voltage induced in a coil

lying in the vicinity of coil is 63.75 volts. If the coefficient of coupling between the coils is0.75, find Self inductance of the two coils, Mutual Inductance and Number of turns in the

second coil. (16 Marks)

7. a) Two identical coupled coils in series has an equivalent inductance values of 0.084H and0.0354 H, Find the values of L1, L2, M and K . (8 Marks)

b) In the circuit find the phasor voltage V2. (8 marks)

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8. In a series fed double tuned circuit , a maximum voltage gain of 20 was obtained at aresonant frequency of 106 radian/sec, the capacitance in the primary circuit is 2 µF. The

maximum output voltage at resonance is 50 volts. Assume that the primary and secondary

resistances are 1 ohm and 4 ohm respectively.Calculate

i. Supply voltage.ii. The primary and secondary self inductances.

iii. The critical corefficient of coupling.

iv. The capacitance in the secondary circuit. (16 marks)

UNIT IV TRANSIENT RESPONSE FOR DC CIRCUITS

Part – A- Two marks questions

1. What is transient and why transients occur in electric circuits?

2. Define time constant of RL circuit.

3. Define time constant of RC circuit.

4. What is damping ratio and critical dam?

5. What is critical resistance?6. What is natural and damped frequency?

7. What is an initial condition?

8. What is the steady state value?

9. What are critical frequencies? Why they are so called?

10. Distinguish between steady state and transient response.

11. What is meant by two port network?

12. Define driving point impedance and transfer impedance of a network.

13. Define the short circuit driving point admittance of a two port network.

14. Define hybrid parameters of a two port network.

15. Express Y parameters in terms of Z parameters16. Part – B 16 marks questions

1. Derive the expression for RLC transient circuits (16)

2. A series RL circuit with R =30ohm and L =15H has a constant voltage E =60v is applied at t=0

as shown. Determine the current I, voltage across the resistor and inductor.(16)

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3. Find how long it takes after the key is closed before the total current from the supply reaches

25mA when v=10volt,R1 =500ohm, R2 =700 ohm and c=100µF.(16)

4. In the circuit shown in figure, Find current i(t) assume initial charge in the capacitor is zero (16)

5. In the circuit shown in figure, Find the transient current when the switch is closed at t=0.Assume

zero initial conditions(16)

6. For a source free RLC series circuit the initial voltage across C is 10v and the initial currentthrough L is zero if L=20mH,C=0.5µF and R= 100 ohm, Evaluate i(t) (16)

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7. The Z-parameters of a two port network are Z11 =25ohm, Z22=40ohm, z12=z21=10ohm.Find

the Y-parameters (16)

8. For a two port network Y parameters are Y11=0.1mho,Y22 =0.05mho, Y12=Y21=-0.02mho.Calculate the Z-parameters for the same network.(16)

UNIT V THREE PHASE CIRCUITSPart

– A- Two marks questions

1. What is phase sequence?

2. Write the relation between the line and phase value of voltage and current in a balanced star

connected load.

3. Write the relation between the line and phase voltage of voltage current in a balanced delta

connected load.

4. Write the relation between the power factor and wattmeter readings in two-wattmeter method of

power measurement.

5. In three phase circuit, what do you mean by balanced load?

6. When a three phase supply system is called balanced supply system?

7. List any two advantages of 3-phase system over 1-phase system.

8. Compare balanced and unbalanced network.

9. Write the expression for the power factor in balanced three phase circuit.

10. When do the two watt meters read equal in the two watt meter method of 3 phase power

measurement?

11. Write the expressions for the instantaneous emfs in a 3 phase circuit.

12. What will be the readings of the two watt meters used for measurement of power in a three phase

circuit at unity power factor?

13. When does one watt meter read zero in the two watt meter method of three phase power

measurement?14. Write the formula to obtain multiplication factor for a given watt meter.

15. How can a watt meter be used to measure reactive power?

16. Part – B 16 marks questions

1. With a neat circuit and phasor diagram explain the three phase power measurement by two

wattmeter method and also derive the expression for Power Factor. (16)

2. A balanced star connected load of (8+j6) ohms per phase is connected to a three phase 230V, 50

Hz supply. Find the line current, PF, power, reactive Volt amperes and total volt amperes. (16)

3. A three phase delta connected load has Zab = (100+j0) ohms, Z bc = (-j100) ohms and Zca =

(70.7+j70.7) ohms and is connected to a balanced three phase 400V supply. Determine the line

currents Ia, I b, Ic. Assume the phase sequence as abc. (16)

4. a) A balanced delta connected load takes a line current of 15A when connected to a balanced 3

phase 400V system. A watt meter with its current coil in one line and potential coil between the

two remaining lines read 2000 Watts. Describe the load impedance. (8)

b) Determine the power and power factor, if the two watt meters read. (i) 1000 watts each, both

positive. (ii) 1000 Watts each of opposite sign. (8)

5. The power input to a 2000V, 50 Hz three phase motor running on full load at an efficiency of

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90% is measured by two watt meters which indicate 300KW and 100KW respectively. Calculate

(i) input power (ii) power factor (iii) line current (iv) HP output. (16)

6. Three impedance each of 10 ohms resistance and 5 ohms inductive reactance are connected in

delta to a 400V, 3 phase supply. Determine the current in each phase and in each line. Calculate

also the total power drawn from the supply and the p.f of the load. (16)

7. A wye load with ZA=3+j0, ZB=2+j3 and ZC=2-j1 ohms is connected to a 3 phase 4 wire, 100

volts, CBA system. Find the currents in all the four lines. (16)

8. Determine the ine currents for the unbalanced delta connected load consisting of ZRY = (30+j40),

ZYB = (8-j4) and ZBR = (15+j12) ohms. Assume the phase sequence to be RYB, E=200 volts.

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EE6201-CT-U1-5-QB