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I C. S. Exam

Sl. No. C-DTN-L-FFA
0

:ELECTRICAL ENGINEERING Paper-I
I Time Allowed: TIlree Hours 1·1 300 1
INSTRUCTIONS.
Each question is printed both in Hindi and
,in
..Answers must .be written in medium specified in the Admission Certificate issued ..to you, which must lJe stated. clearly on the cover of the answer-book in the space
• proiJided for the purpose. No" markS will be given for the answers written in a medium other than that .specified' in the Admission Certificate.
'Cahaidates should attempt Questiori,:·Nos. 1 and 5 which are·compulsory, and any three of the remaining questio11S selecting at least. one question from each Section.
The number of marks carried By each
.question: is indicated at the' end of the question.
Assume suitable data if considered
necessary an4'i1ldicate the same clearly.

Symbols/Notations carry 'their usual meanIngs, unless otherwise indicated.
"
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Section-A

1. A storage battery has a no-load terminal voltage of 6 V. When the current through the battery is 100 the terminal voltage drops to 5 V. Show a pictorial representation of the battery as a constant current source. 15
Find the Fourier transform of the signum function'. 15
Three small spheres each carrying a charge q are placed on the circumference of a circle of radius r to form an equilateral triangle. Find the electric field and the potential at the centre of the circle. 15
With reference to a BJT, show that dowpc/dowtj<1/0ja must, be satisfied in order to prevent thermal runaway. 15
2. U sing Millman's theorem, find the current I in the IO-ohm resistor In <img src='./qimages/1060-2a.jpg'>
State and maximum power 'prove transfer theorem. 20
The switch S is closed at t 0 in Fig. 2 Using Laplace transforms, find i2 and the voltage across the inductance. 20
<img src='./qimages/1060-2c.jpg'>
A power 'signal has a power Sf Find .the power density spectrum of the signal df/dt.
Fig. 3 shows two identical parallel­plate capacitors connected to a battery with. switch S closed. The switch S is opened and. the free space between the plates of the capacitors is. filled with a dielectric of 'dielectric coefficient K 2. Find the ratio of the total electrostati energy stored in both capacitors after the introduction of the' dielectric. 20
<img src='./qimages/1060-3b.jpg'>
A uniform plane wave is, by the phasor H 2e(-jO·l1tz) . Q.y A/m. If the velocity of the wave is 2 x 108 and the relative permeabiUty is 1· determine the frequency, relative permittivity, wavelength and electric intensity. 20
4. Using an OP-AMP, several capacitors of ,0·1 IJ.F number of resistances of your choice, design a· phase-shift ,oscillator to oscillate at 100 ..Hz. 20
Using IC 555 and other suitable components, draw the circuit diagram of a missing pulse detector and explain its working. 20
For the current mirror shown in Fig. 4 determine the emitter current of transistor 03 (Assume 100 and VBE O· 6"V) 20 <img src='./qimages/1060-4c.jpg'>

Section-B
Implement the fol1owing 15
Half-adder using ,basic gates
T flip-flop using J-K flip-flop
2 to 4 decoder using lx4 de multiplexers
Draw torque -vs. induction motor,. slip -curve for an
Specify the condition for a DC machine so that its rotor does not draw any current.
What will be the· effect on V.A rating of a transformer if we double the supply frequency? 15
Draw circuit diagram for,the following: 15
Three-phase FW bridge 'rectifier
Boost switching regulator
DC trigger circuit for an SCR
Specify the types of modulation used in the following and give reason for the same: 15
TV-video signal
TV-sound signal
Long-distance telephone system

6 Convert decimal :number 40 into binary and hexadecimal numbers. 20
draw symbolic representation for +ve edge triggered clock input in a flip-flop and ffiMk' transition time by an arrow in clock. input waveform 'for it. 20
write the full form. of FPGA and explain 'why it is useful for Prototyping of digital circuits. 20
7. A DC motor with permanent magnet field is running,;with 200' V supply and consuming 2A currenL A voltmeter is connected 'across its armature and DC supply is disconnected. The voltmeter reads .. ,190 V just after, disconnection of DC ,the armature resistance of the machine... .. 20
Explain working"of a synchronous machine as.a synchronous. condenser. 20
Why are the frequency. and voltage both varied in the same proportion for a full-range variabJe speed control of ACmotor?6. 20

8. The RMS value of the antenna current before amplitude modulation is lOA and after modulation is 12 A. Calculate the percentage -modulation. Assume that there is no distortion. 20
Explain how a PLL can be used in FM detection. In what way is this scheme better than the ratio detector? 20
A receiver, connected to an antenna of resistance 50 ohms, has an equivalent noise resistance of 30 ohms. Find the noise figure of the receiver in dB. 20