WBUT Exam Papers EE Basic Electrical And Electronic Engineering-I B Tech 2nd Sem 2012

WBUT Exam Papers EE

Basic Electrical And Electronic Engineering-I B Tech 2nd Sem 2012


Full Marks : 35

The figures in the margin indicate full marks.

Candidates are required to give their answers in their own words

as far as practicable.                     t

GROUP – A ( Multiple Choice Type Questions )

1 Choose the correct alternatives for any five of the following : 5×1-5

i)              In a three phase balanced system, line voltage makes an angle with phase voltages

a) 30°                                             *>) 60°

c)          90° ,        120°-

f* <

ii)            The speed in which stator magnetic field rotates is called

a)             actual speed

synchronous speed

c)             slip speed

d)            super-synchronous speed.


ili) If a d.c. series motor is started at no load, the speed will be

a)           rated speed

b)           zero

d)           half of the rated speed.

iv)          If two static charges having magnitude 1 coulomb each

are placed at 1 m apart in space, the electrostatic force developed between the charges is

a)             90 x 10 0 newtons Jrf) 9 x 10^ newtons

c)             0-9 x 10J newtons d) 0.

v)           The regulation of a transformer is negative, if the load at the secondary side is

a)            resistive

b)           inductive

‘c) capacitive

d)            combination of resistive, inductive & capacitive, vi) Which of the following in a four-wire system ?

a)            Delta with neutral

b)           Star with neutral

c)            Both delta & star

d)           Any combination of four wires.

Answer any two of the following.               2×5= 10

Prove that the efficiency of transformer is maximum when iron loss is equal to copper loss.

Derive an expression for capacitance of a cylindrical capacitor, assuming grounded outer surface.

What is a three-phase balanced A.C. system ? Show that, in

a three-phase balanced a.c. circuit, the sum of current in the neutral is zero.

5. Derive the expression of torque of a ci.c.


Answer any two of the following. 2×10 = 20

6- a) Explain the principle of operation of a transformer under loaded condition.

b)            A 200 kVA transformer has 400 turns on the primary & 40 turns on the secondary winding. The primary is connected to 2 ‘kV, 50 Hz supply. Find the full load primary & secondary current, secondary emf & the maximum flux in the core. Neglect leakage drop & no­load primary current.                                                         , ~

4 + b

7. j#’ Explain the open circuit characteristics ( OCC ) of a DC generator.

bj An 8-pole, 400 V shunt motor has 960 wave connected armature conductors. The full load armature current is 40 A & flux per pole is 0 02 Wb. The armature resistance is 01 Q and the contact drop is 1 V per brush. Calculate the full load speed of the motor.

c)            Why starter is needed to start a d.c. motor ?


°                                   [ Turn over


8- a) A three-phase Induction motor is self -starting. Explain.

Obtain the relation between the slip and frequency of the rotor induced ernf.                                 ~

A 4-pole, 3-phase, 275 kW, 440 V, 50 Hz induction gig or in running with a slip of 4%. Find_____ –

i)                    synchronous speed

ii)                  rotor speed

m) frequency of the rotor induced ernf. < 3 + 2 + 5

Explain the principle of measurement of balanced

P P°wer ^ 2-Wattmeter method. Draw the neat circuit & phasor diagrams.

These equal impedances ( 6 + j8 ) £2 are connected a cross a 400 V, 3-phase, 50 Hz supply. Calculate 1

») the line current & the phase current W) power factor

Hi) active & reactive drawn by load per phase. 5 +


,                Full Marks : 35

The figures in the margin indicate full marks.

Candidates are required to give their answers in their own words

as Jar as practicable.

GROUP – A { Multiple Choice Type Questions )

1. Choose the correct alternatives for any fwe of the following :      s x i = s

i)            An ideal Op-Amp is an ideal

a) voltage controlled current source

^ voyage controlled voltage source

c)             current controlled current source

d)            current controlled voltage source.

11) The AND function can be realized by using only n number of NOR gates. What is n equal to ?

a)                                                                                         2        b) 3


iii)          The Boolean expression ABC + ABC + ABC + ABC is of

yrf OR gate                             b) AND gate

c) EX-NOR gate                       d) EX-OR gate.

iv)          Which of the following statements is/are correct in

regard to excess 3 code ?


a)            It is a BCD code

b)            It is an unweighted code

c)            It is a self complementing codc

d)           All of these.

v)            In Barkhausen criterion, phase of Aji is a) 0°

Iff multiple of 180° u

c)            0° or multiple of 180c

d)           0° or multiple of 360c

vi)          In inverting amplifier circuit if input & feedback resistances are 1 kQ and 3 kQ, respectively, i/p voltage is 3 volt and power supply voltage is ± 6V, then thf output voltage of Op-Amp is

a) – 6 volt                                b) +6 volt

– 9 volt                            d) +9 volt.

Answer any two of the following.                2×5= 10

2/ Mention the advantages and disadvantages of negative feedback amplifier.

Dis< ,ss the operation of op-amp as an integrator.

Implement the function F = (AB + CD) using NAND


bl (1I011)2 -(?),o


“‘rite down the basic difference between enhancement type and depletion type MOSFETs.

a i What is virtual ground of an Op-Amp ?

bl Draw and explain the voltage comparator circuit using Op-Amp.


Answer any two of the following. 2 x 10 = 20

What is the effect of negative feedback on output impedance and phase distortion ?

bl An amplifier has a voltage gain of -100. The feedback ratio is – 0 04. Find

i the voltage gain with feedback

ii)            the amount of feedback in dB

«i) the output voltage of the feedback amplifier for an input voltage of 40 raV

iv)           the feedback factor

vj the feedback voltage.


7. . al Explain the basic operation of depeletion type n channel MOSFET with a suitable diagram.

What are the basic differences between BJT and FET ?

c)            /As  Vgs is changed from 0 V to 02 V keeping VDS constant, ID of the FET drops from 10*25 mA to

9-65 mA. What is the transconductance of the FET ? If the a.c. drain resistance is 32 k£2, find also the amplification factor of the FET.

d)           What do you mean by pinch off voltage for n-channel JFET ?        4 + 2 + 2 + 2

a) If the feedback resistance R j. is replaced by a diode for

a negative feedback amplifier using Op-Amp, then derive the expression of o/p voltage vq for it. Also,


mention the type of application for this modification.

* ■ f .

4 + 1






b)             For the given circuit find the output voltage v .

axa ilka 8KX1

9. Write short notes on any two of the following :                                                                                                          2×5

a)             Topologies of feedback amplifier

b)             Summing amplifier

c)              CMOS

d)             Design of exclusive-OR gate.

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