AU First Year Engineering (Semester 2)
Circuit Theory
May 2014
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

1 Find the equivalent resistance of the circuit shown in Fig

2 M

2 Define RMS voltage.
2 M

3 What is reciprocity theorem?
2 M

4 Why do you short circuit the voltage source and open the current source when you find Thevenin's voltage of a Network?
2 M

5 Define quality factor in the resonant circuit.
2 M

6 Determine the quality factor of a coil for the series resonant circuit consisting of R=10 ohm, L=0.1h, and C=10 microfarad.
2 M

7 Distinguish between natural and forced response.
2 M

8 What is the time constant for RL and RC circuit?
2 M

9 Write the effect of power factor in energy consumption billing
2 M

10 Distinguish between unbalanced source and unbalanced load.
2 M

11 (a) (i) Find the current I and voltage across 30 ? of the circuit shown in Fig. 11 (a) (i).

8 M
11 (a) (ii) Determine the current in all the resistors of the circuit shown in Fig. 11 (a) (ii).

8 M
11 (b) (i) Determine the current through each resistor in the circuit shown in Fig. 11(b) (i)

6 M
11 (b) (ii) When a dc voltage is applied to a capacitor, voltage across its terminals is found to build up in accordance with vc=50 (1-e-100t). After 0.01 S the current flow is equal to 2 mA.
(1) Find the value of capacitance in farad.
(2) How much energy stored in the electric field?
10 M

12 (a) (i) Determine the current in the 5? resistor in the network shown in Fig. 12 (a) (i).

8 M
12 (a) (ii) Find out the current in each branch of the circuit shown in Fig.12 (a) (ii)

8 M
12 (b) (i) Determine current in each mesh of the circuit shown in Fig 12 (b) (i)

8 M
12 (b) (ii) Determine the voltage at each node of the of the circuit shown in Fig. 12 (b) (ii)

8 M

13 (a) For the circuit shown in Fig 13(a), determine the impedance at resonant frequency, 10 Hz above resonant frequency, and 10Hz below resonant frequency.

16 M
13 (b) Explain that how to derive Q factor of parallel resonance.
16 M

14 (a) A series RL circuit with R=30? and L=15H has a constant voltage V=60 v applied at t=0 as shown in Fig. 14(a). Determine the current i, the voltage across resistor and the voltage across the inductor.

16 M
14 (b) The circuit shown in Fig. 14 (b) consists of resistance, inductance and capacitance in series with 100V DC when the switch is closed at t=0. Find the current transient.

16 M

15 (a) (i) A symmetrical three-phase; three wire 440V supply to a star connected load. The impedance in each branch are ZR =2+j?, ZY=1-j2? and ZB=3+j4?. Find its equivalent delta connected load.
8 M
15 (a) (ii) A three phase, balanced delta-connected load 4+j? is connected across a 400V, 3? balanced supply. Determine the phase currents and line currents. (Phase sequence is RYB).
8 M
15 (b) (i) A symmetrical three-phase, three 400V, supply to a star connected load. The impedance in each branch are ZRY=10?30? ?, ZYB=10?45? ? and ZBR=2.5?60? ?. Find its equivalent star-connected load.
8 M
15 (b) (ii) A balanced star connected load having an impedance 15+j20? per phase is connected to 3?, 440V, 50Hz. Find the line current and power absorbed by the load.
8 M

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