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Reg. No. :

Question Paper Code : U4004

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) Maximum : 100 Marks

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Time : Three hours

PART A — (10 × 2 = 20 Marks)

The resistance of two wires is 25 Ω when connected in series and 6 Ω when joined in parallel. Calculate the resistance of each wire.

2.

A series RLC circuit has R = 25 Ω , 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

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1.

4.

State maximum power transfer theorem for d.c. circuits.

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.

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5.

(a)

(i)

Determine the current in the 4 Ω branch in the circuit shown in Fig. (11. a(i)). Use mesh analysis method. (8)

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11.

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PART B — (5 × 16 = 80 Marks)

Fig. (11. a(i))

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For the network shown in Fig. (11. a(ii)), find VS which makes I 0 = 7.5 mA. Use node voltage method. (8)

Fig. (11. a(ii))

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(ii)

Or Using the mesh current method, obtain the voltage V x in the network of Fig. (11. b). (16)

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(b)

Fig. (11. b)

(a)

(i)

Obtain the current in each resistor in Fig. (12. a(i)) using network reduction methods. (6)

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12.

Fig. (12. a(i)) 3

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In the network shown in Fig. (12. a(ii)) determine the Current I. (10)

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(ii)

Fig. (12. a(ii))

Using the principle of superposition, calculate the Current I in the network of Fig. (12. b). (16)

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(b)

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Or

Fig. (12. b) (a)

For a two–branch parallel circuit R L = 15 Ω, R C = 30 Ω, X C = 30 Ω, E = 120 V and f = 60 Hz. For the condition of resonance, Calculate

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13.

the two values of L and

(ii)

the two values of total current.

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(i)

(16)

Or 4

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Calculate the voltage V for the coupled circuit shown in Fig. (13. b) Repeat with the polarity of one coil reversed. (16)

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(b)

50 0

Fig. (13. b) (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)

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14.

Fig. (14. a) Or

A series RC circuit with R = 100 Ω and C = 25 µF 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)

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(b)

(a)

(i)

Derive the expression for the total power in a 3 phase balanced circuit using two wattmeters. (10)

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15.

(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 5

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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)

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(b)

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Fig. (15. b)

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————––––——

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U 4004

CT QP Nov 2009

CT QP Nov 2009