131201(EE 1151) – CIRCUIT THEORY B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2009. Second Semester




Reg. No. :
B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2009
Second Semester
Electrical and Electronics Engineering
EE 2151 — CIRCUIT THEORY
(Common to Electronics and Instrumentation Engineering and Instrumentation and
Control Engineering)
(Regulation 2008)
Time : Three hours Maximum : 100 Marks
Answer ALL Questions
PART A — (10 × 2 = 20 Marks)
1. The resistance of two wires is 25 when connected in series and 6 when
joined in parallel. Calculate the resistance of each wire.
2. A series RLC circuit has R = 25 , L = 0.221 H and C = 66.3 μF with
frequency of 60 Hz. Find the power factor.
3. Convert the current sources into voltage sources in the circuit shown below
4. State maximum power transfer theorem for d.c. circuits.
Question Paper Code : U4004
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2 U 4004
5. Define the term ‘Quality factor’.
6. What is meant by coupling Coefficient?
7. Define the term ‘time constant’.
8. In a series RLC circuit, L = 2H, and C = 5 μF . Determine the value of R to give
critical damping.
9. A 3 phase 400 Volts supply is given to a balanced star connected load of
impedance 8 + j6 ohms in each branch. Find the line current.
10. List out the methods of power measurement in three phase balanced circuits.
PART B — (5 × 16 = 80 Marks)
11. (a) (i) Determine the current in the 4 branch in the circuit shown in
Fig. (11. a(i)). Use mesh analysis method. (8)
Fig. (11. a(i))

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(ii) For the network shown in Fig. (11. a(ii)), find S V which makes
7.5 0 I = mA. Use node voltage method. (8)
Fig. (11. a(ii))
Or
(b) Using the mesh current method, obtain the voltage x V in the network of
Fig. (11. b). (16)
Fig. (11. b)
12. (a) (i) Obtain the current in each resistor in Fig. (12. a(i)) using network
reduction methods. (6)
Fig. (12. a(i))
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(ii) In the network shown in Fig. (12. a(ii)) determine the Current I. (10)
Fig. (12. a(ii))
Or
(b) Using the principle of superposition, calculate the Current I in the
network of Fig. (12. b). (16)
Fig. (12. b)
13. (a) For a two–branch parallel circuit R 15 , R 30 , X 30 , L C C = = =
E = 120 V and f = 60 Hz. For the condition of resonance, Calculate
(i) the two values of L and
(ii) the two values of total current. (16)
Or
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5 U 4004
(b) Calculate the voltage V for the coupled circuit shown in Fig. (13. b)
Repeat with the polarity of one coil reversed. (16)
Fig. (13. b)
14. (a) In the series circuit shown in Fig. (14. a) the switch is closed on position
1 at t = 0 At t = 1 milli second, the switch is moved to position 2. Obtain
the equations for the current in both intervals and draw the transient
current curve. (16)
Fig. (14. a)
Or
(b) A series RC circuit with R = 100 and C = 25μF is supplied with a
source of 200 sin(500t)V. Find the current in the circuit. Assume initial
charge on the capacitor is zero. (16)
15. (a) (i) Derive the expression for the total power in a 3 phase balanced
circuit using two wattmeters. (10)
(ii) The power input to a 2000 V, 50 Hz, 3 – phase motor is measured
by two wattmeters which indicate 300 kW and 100 kW respectively.
Calculate the input power, power factor and the line current. (6)
Or
50 0
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(b) Determine the line currents and the total power for the unbalanced
– connected load Shown in Fig. (15. b). A 3 phase supply, with an
effective line voltage of 240 V is given to the circuit. (16)
Fig. (15. b)
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0
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