EE2151– CIRCUIT THEORY B.E./B.Tech. DEGREE EXAMINATION, MAY/JUNE 2010. Second Semester

Reg. No. :
B.E./B.Tech. DEGREE EXAMINATION, JUNE 2010
Second Semester
Electrical and Electronics Engineering
EE2151 — CIRCUIT THEORY
(Common to Instrumentation & Control Engineering and Electronics &
Instrumentation Engineering)
(Regulation 2008)
Time : Three hours Maximum : 100 Marks
PART A — (10 × 2 = 20 Marks)
1. In the figure 1 shown, find the value of I.
Figure 1
2. Find the equivalent resistance between A and B in figure 2.
Figure 2
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3. Find the equivalent current source for the circuit shown in figure 3.
Figure 3
4. State maximum power transfer theorem in a dc circuit.
5. In a series RLC circuit, if the value of L and C are 100μH and 0.1 μ f
respectively, find the resonance frequency in HZ.
6. In a coupled circuit having two coils, the value of 1 2 L , L and K are 5 mH,
10 mH and 0.8 respectively where K is the coefficient of coupling. Find the
mutual inductance between the two coils.
7. A series RL circuit with R = 100 and L = 20H has a dc voltage of 200V
applied through a switch at t = 0 . Assuming the initial current through the
inductor at t = 0 is zero, find the current at t = 0.5 sec.
8. What is the condition to be present in a series RLC circuit to make the circuit
critically damped?
9. In the circuit shown in figure 9, find the rms value of line current and phase
voltage.
Figure 9
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10. In the circuit shown in figure 10, find the total power consumed by the 3φ
Figure 10
PART B — (5 × 16 = 80 Marks)
11. (a) In the circuit shown in figure 11 (a), find the different mesh currents,
power delivered by each source and the current through RL. (16)
Figure 11 (a)
Or
(b) In the circuit shown in figure 11 (b), find the different node voltages and
the currents 1 2 I , I and 3 I . (16)
Figure 11 (b)
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12. (a) In the circuit shown in figure 12 (a), find
(i) the equivalent resistance between P and Q. (7)
(ii) the total current from the 240V source. (2)
(iii) the current through the 18 resistor. (7)
Figure 12 (a)
Or
(b) (i) In the following circuit shown in figure 12 (b), (i) find the current
through 5 by Thevenin’s theorem. (8)
Figure 12 (b) (i)
(ii) Find the value of L R at which maximum power is transferred to
L R and hence the maximum power transferred to L R in the circuit
shown in figure 12 (b) (ii). (8)
Figure 12 (b) (ii)
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13. (a) A series RLC circuit with R = 10 , L = 10 mH and C = 1 μ f has an
applied voltage of 200 V at resonance frequency. Calculate the resonant
frequency, the current in the circuit and the voltage across the elements
at resonance. Find also the quality factor and band width for the circuit.
(16)
Or
(b) In the circuit shown in figure 13 (b), find the value of 1 I and 2 I and also
the real power supplied by each source. (16)
Figure 13 (b)
14. (a) In the circuit shown in figure 14 (a), the switch S is closed at time t = 0 in
position 1 and changed over to position 2 after one millisecond. Find the
time at which the current is zero and reversing its direction. Assume that
the change over of switch from position 1 to 2 takes place in zero time.
Figure 14 (a)
Or
(b) In the circuit shown in figure 14 (b), find the expression for current if the
switch is closed at t = 0 and the value of current at t = 1 millisecond.
Assume initial charge on the capacitor is zero. (16)
Figure 14 (b)
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15. (a) (i) Two wattmeters are connected to measure the power in a 3φ , 3 wire
balanced load. Determine the total power and power factor if the
two wattmeters read (1) 1000 w each, both positive (2) 1000 w each,
of opposite sign. (8)
(ii) Determine the line currents for the unbalanced delta connected
load shown in figure 15 (a) (ii) phase sequence is RYB. (8)
Figure 15 (a) (ii)
Or
(b) An unbalanced star-connected load is supplied from a 3φ , 440V ,
symmetrical system. Determine the line currents and the power input to
the circuit shown in figure 15 (b). Assume RYB sequence. Take phase
voltage Rn V as reference in the supply side. (16)
Figure 15 (b)
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