318(S)

March 2021

ELECTRICAL CIRCUIT & NETWORK

Time Allowed: 3 Hours Full Marks: 70

Answer to Question No.1 is compulsory and Answer any five questions from the rest.

1. A. Answer the following questions in one or two sentences (any ten): 1x10

i) Write some applications of Maximum power transfer theorem.

ii) What is transient state?

iii) What are the advantages of ABCD matrix?

iv) Find the current flowing through an element if the charge flow is given by: q(t) = (t + 2)
mC.

v) A voltage source of 20 sin πt V is connected across a 5-kΩ resistor. Find the current
through the resistor and the power dissipated.

vi) Evaluate these complex numbers: (40∟ 50 + 20∟− 30).

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

viii) Why the capacitor is called non-dissipative passive element?

ix) Write the expression for impedance in the RLC series circuit.

x) Find the Equivalent Current Source for a voltage source of 10 Vin Series with A 60ohm
Resistance.

xi) What is the limitation of superposition theorem?

xii) State Norton’s theorem.

B. Choose the correct answer from the given alternatives (any ten): 1x10

i) Thevenin’s equivalent circuit consists of- (a) current source with parallel resistance
(b) voltage source with series resistance (c) current source with series resistance (d)
voltage source with parallel resistance.

ii) Norton’s theorem is the dual of- (a) tellegan’s theorem, (b) millman’s theorem,
(c) thevenin’s theorem, (d) maximum power theorem.

iii) Maximum power is transferred when load impedance is equal to- (a) source impedance,
(b) source current, (c) source voltage,(d) source power.

iv) Transient behavior occurs in any circuit when- (a) there are sudden changes of applied
voltage, (b) the voltage source is short circuited,(c) the circuit is connected or
disconnected from the supply, (d) all of the above.

v) The Magnitude of current at resonance in RLC circuit -(a) depends upon the magnitude of
R, (b) depends upon the magnitude of L, (c) depends upon the magnitude of C,(d) depends
upon the magnitude of R, Land C.

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 vi) Laplace transform analysis gives- (a) Time domain response only, (b) Frequency domain
response only, (c) Both A & B, (d) None of these.

vii) Two port network has________ number of terminals.- (a) 1, (b) 2, (c) 3, (d) 4.

viii) In voltage source, internal resistance always in- (a) Series, (b) Parallel, (c) Both, (d) none.

ix) A sinusoidal current has peak value of 12A. What is its average value?- (a) 8.65A,
(b) 6.94A, (c) 5.39A, (d) 7.64A.

x) The nodal method of circuit analysis is based on- (a) kirchoff’s current law, (b) kirchoff’s
voltage law, (c) Ohms law, (d) voltage division.

xi) The equivalent current-source representation for a voltage-source with open circuit voltage
12 V and internal resistance 3 ohms is- (a) a current-source of strength 4A in shunt with a
resistance of 6Ω, (b) a current-source of strength 4A in series with a resistance of 3Ω, (c) a
current-source of strength 4A in shunt with a resistance of 3 ohms, (d) a current-source of
strength 4A in shunt with a resistance of 36 ohms.

xii) Super position theorem is valid only for- (a) nonlinear, (b) linear circuits, (c) both, (d)
none of the above.

2. a) State and proof final value theorem.

b) In the following circuit, steady state exists when switch S is in position 1. At t=0, it is moved to
position 2. Obtain the expression for current using Laplace transformation. 4+6

3. a) Define resistance, reactance and impedance.

b) For the circuit shown find the current in various branches by nodal analysis. 3+7

4. a) Explain the transmission parameters of a two port network?

b) Determine current flowing through 5Ω resistor in the circuit shown below. Usetransformation
technique. 5+5

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5. a) Define and explain Thevenin’s theorem.
b) Using Thevenin’s theorem, find the current through 2.5 ohms resistance in the circuit shownin the
figure. 3+7

6. a) Give one application of maximum power transfer theorem.

b) For the circuit shown in figure, find the value of RL for maximum power transfer. What will be the
value of maximum power? 2+8

7. a) Deduce an expression for the growth of current in an inductive circuit when connected to a d.c.
supply.
b) A coil of 10 H inductance and 5Ω resistance is connected in parallel with a 20 Ωresistor across a
100-V d.c. supply which is suddenly disconnected. Find (i) the initial current after switching (ii)
the voltage across the 20 Ωresistor after 0.3 sec. 4+6

8. Find the impedance, current and power factor of the following series circuits and draw thecorresponding
phasor diagrams i) R and L ii) R and C iii) R, L and C. In each case theapplied voltage is 200volts and the
frequency is 50Hz. R = 10 Ω, L =50 mH, C= 100 μF. 10

9. a) Define quality factor.

b) A resistance of 20 ohm, an inductor of 0.2 H and a capacitor of 100 µF are connected in series
across 220 V, 50 Hz mains. Determine the following (i) impedance (ii) current (iii) voltage across
R, L and C (iv) power in watts and VA (v) p.f and angle of lag. 3+7

10. a) Define the term bandwidth and selectivity

b) Perform the following operation and express the final result in the polar form: 5L 30º + 8 L -30º.
c) Draw a power triangle and explain the term active power, reactive power and apparent
power. 3+3+4

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