WBUT Question Papers EC
Circuit Theory & Networks B Tech Sem Third 2008 Dec
Time : 3 Hours ]
( Full Marks : 70
GROUP – A ( Multiple Choice Type Questions )
- Choose the correct alternatives for any ten of the following : 10 x 1 = 10
i) Maximum power transfer occurs at efficiency of a) 100% ‘ b) 50%
c) 25% . d) 75%. Q___
ii) A periodic waveform possessing half-wave symmetry has no a) odd harmonics b) even harmonics
c) cosine terms d) sine terms. ____
iii) The impedance of an ideal current source should be
a) 0 .
c) greater than 0 but less than infinity
d) none of these
iv) In R-L circuit, the phase angle difference between voltage & current is
a) 30° b) 90*
c) 180° d) greater than 0° but less than 90°.
v) Unit step function is first derivative of
a) ramp function b) impulse function
c) gate function d) parabolic function.
vi) After closing the switch ‘s’ at t = 0. the current t ( t ) at any instant in the network shown
lS given by
a) 10 + 10 e100r b) 10 – 10 e,00r
vii) When compared to a first order low psss filter, a second order low pass filter has
a) lower voltage gain b) higher voltage gain
c) faster drop in filter response d) higher cut-off frequency.
viii) A cut set schedule gives relation between
a) branch currents & link currents
b) branch voltages & tree branch voltages
c) branch voltages & link voltages
d) branch currents & tree currents.
ix) The equation Y = mx + c is
a) linear b) non-linear
c) parabolic d) none of these.
x) Graphical representation of u ( a – t)
xl) A two port network is reciprocal if & only if
a) Zn =Z22 b) BC-AD = -1
c) Yl2=Y2l »
d) h12 = h 21-
xii) Given VTH = 20 V & RTH = 5Q. the current in the load resistance of a network is
GROUP -B ( Short Answer Type Questions )
Answer any three ot the following. 3×5= 15
For an RL series circuit shown in the figure 1 with R = 2Q & L = 1H and no tnit.ai current in the inductor. A voltage V= 4e~l volts is applied at t = 0. Find expression for the resulting current in the circuit tor ( > 0 using Liiplace transform method
- a) Define incidence matrix.
- b) For the graph shown in figure 2, find the complete incidence matrix.
- What should be the value of Z2 for maximum power to be delivered in the circuit shown in fig. 3
- In a linear circuit consisting of R = 9J2 & L = 8 mH, a current.
i = 5 + 100 sin ( lOOOt + 45′ ) + 100 sin ( 3000t + 60’ ) amps is flowing. Find the equation of applied voltage.
- Measurements were made on two terminal network shown in figure 4.
a) With terminal pair 2 open, a voltage of 100 < 0* volts applied to terminal pair 1 resulted in I, = 10 < 0* amps & V2 = 25 < 0‘ volts.
b) With terminal pair 1 open, the same voltage applied to terminal pair 2 resulted in I2 = 20 < 0‘ amps & V, = 50 < 0′ volts.
Write the loop equations for this network and also find the driving point & transfer impedances. •
GROUP -C ( Long Answer Type Questions )
Answer any three of the following. 3 x 15 = 45
- a) Solve the circuit current'( shown in the figure 5 using Thevenin’s theorem
Verify the result obtained by Norton s theorem,
b) Obtain the output voltage V 0 across X – Y terminal for the circuit shown in
b) Find the Fourier transform of an exponential voltage waveform given by
u( t) = V0e-‘fort>0
= 0 for t < 0. 10 + 5
What are transmission parameters ? Where are they most effectively used ? Calculate the ABCD parameters of the network shown in figure 8.
c) Find the hybrid parameters of the circuit given in figure 9.
- a) Differentiate between active and passive filters.
b) Find out the cut-off frequency of the following low-pass second order active filter shown in figure 10.
c) Draw the circuit diagram of a first order high-pass active filter and find out the expression of the cut-off frequency. 5 + 6 +
a) State superposition theorem. For the network shown in figure 11. calculate current throughout the impedance ( 3 + J 4 ) ohm using superposition theorem.
b) In the given circuit of figure 12. find the reading of the voltmeter V. Interchange the current source and voltmeter and verify the Reciprocity theorem.