Electrical Engineering - 2009 Unsolved Paper

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ELECTRICAL ENGINEERING - UNSOLVED PAPER - 2009

SECTION – I

 Single Correct Answer Type
 There are five parts in this question. Four choices are given for each part and one of them is

correct. Indicate you choice of the correct answer for each part in your answer-book by

writing the letter (a), (b), (c) or (d) whichever is appropriate

01 Problem

The pressure coil of a dynamometer type wattmeter is

a. highly inductive
b. highly resistive
c. purely resistive
d. purely inductive

02 Problem

The measurement system shown in the figure uses three sub-systems in
cascade whose gains are specified as G1, G2 and (I/G3). The relative small errors
associated with each respective subsystem G1, G2 and G3 are 1, 2 and 3 .The
error associated with the output is:

a. 1+ 2 + (1/ 3)
b. (( 1 . 2)/ 3)

c. 1 + 2 - 3

d. 1 + 2 + 3

03 Problem

The following circuit has a source voltage Vs as shown in the graph. The current
through the circuit is also shown.

The element connected between a and b could be

a. b.

c. d.

04 Problem

The two inputs of a CRO are fed with two stationary periodic signals. In the X-Y
mode, the screen shows a figure which changes from ellipse to circle and back
to ellipse with its major axis changing orientation slowly and repeatedly. The
following inference can be made from this.

a. The signals are not sinusoidal
b. The amplitudes of the signals are very close but not equal
c. The signals are sinusoidal with their frequencies very close but not equal
d. There is a constant but small phase difference between the signals

05 Problem

The increasing order of speed of data access for the following devices is
i. Cache Memory
ii. CDROM
iii. Dynamic RAM
iv. Processor Registers
v. Magnetic Tape

a. (v), (ii), (iii), (iv), (i)
b. (v), (ii), (iii), (i), (iv)
c. (ii), (i), (iii), (iv), (v)
d. (v), (ii), (i), (iii), (iv)

06 Problem

A field excitation of 20 A in a certain alternator results in an armature current of
400A in short circuit and a terminal voltage of 2000V on open circuit. The
magnitude of the internal voltage drop within the machine at a load current of
200A is

a. 1V
b. 10V
c. 100V
d. 1000V

07 Problem

The current through the 2 kΩ resistance in the circuit shown is

a. 0mA
b. 1mA
c. 2mA
d. 6mA

08 Problem

Out of the following plant categories
i. Nuclear
ii. Run-of-river
iii. Pump Storage
iv. Diesel
The base load power plants are

a. (i) and (ii)
b. (ii) and (iii)
c. (i), (ii) and (iv)
d. (i), (iii) and (iv)

09 Problem

For a fixed value of complex power flow in a transmission line having a sending
end voltage V, the real power loss will be proportional to

a. V
b. V2
c. 1/V2
d. 1/V

10 Problem

How many 200W/220V incandescent lamps connected in series would
consume the same total power as a single 100W/220V incandescent lamp?

a. not possible
b. 4
c. 3
d. 2

11 Problem

A Linear Time Invariant system with an impulse response h(t) produces output
y(t) when input x(t) is applied. When the input x (t ) is applied to a system with
impulse response h(t ), the output will be

a. y(t)
b. y(2(t - ))
c. y(t - )
d. y(t - 2 )

12 Problem

The nature of feedback in the opamp circuit shown is

a. Current - Current feedback
b. Voltage - Voltage feedback
c. Current - Voltage feedback
d. Voltage - Current feedback

13 Problem

The complete set of only those Logic Gates designated as Universal Gates is

a. NOT, OR and AND Gates
b. XNOR, NOR and NAND Gate
c. NOR and NAND Gates
d. XOR, NOR and NAND Gates

14 Problem

The single phase, 50Hz, iron core transformer in the circuit has both the
vertical arms of cross sectional area 20cm2 and both the horizontal arms of
cross sectional area 10cm2. If the two windings shown were wound instead on
opposite horizontal arms, the mutual inductance will

a. double
b. remain same
c. be halved
d. become one quarter

15 Problem

A 3-phase squirrel cage induction motor supplied from a balanced 3-phase
source drives a mechanical load. The torque-speed characteristics of the motor
(solid curve) and of the load (dotted curve) are shown. Of the two equilibrium
points A and B, which of the following options correctly describes the stability
of A and B?

a. A is stable B is unstable
b. A is unstable B is stable
c. Both are stable
d. Both are unstable

16 Problem

An SCR is considered to be a semi-controlled device because

a. it can be turned OFF but not ON with a gate pulse
b. it conducts only during one half-cycle of an alternating current wave
c. it can be turned ON but not OFF with a gate pulse
d. it can be turned ON only during one half-cycle of an alternating voltage
wave

17 Problem

The polar plot of an open loop stable system is shown below. The closed loop
system is

a. Always stable
b. Marginally stable
c. Unstable with one pole on the RH s-plane
d. Unstable with two poles on the RH s-plane

18 Problem

The first two rows of Routh's tabulation of a third order equation are as
follows.
S3 2 2
S2 4 4. This means there are

a. two roots at s = ±j and one root in right half s-plane
b. two roots at s = ±j2 and one root in left half s-plane
c. two roots at s = ±j2 and one root in right half s-plane
d. two roots at s = ±j and one root in left half s-plane

19 Problem

The asymptotic approximation of the log-magnitude vs frequency plot of a
system containing only real poles and zeros is shown. Its transfer function is

a. 10( s 5)
s(s 2)(s 25)

1000( s 5)
b. 2
s (s 2)(s 25)

c. 100(s 5)
s(s 2)(s 25)

80( s 5)
d. 2
s (s 2)(s 25)

20 Problem

The trace and determinant of a 2 x 2 matrix are known to be -2 and -35
respectively. Its eigen values are

a. -30 and -5
b. -37 and -1
c. -7 and 5
d. 17.5 and -2

21 Problem

The following circuit has R = 10 Ω, C = 10 μF R. The input voltage is a sinusoid
at 50Hz with an rms value of 10V. Under ideal conditions, the current is from
the source is

a. 10π mA leading by 90°
b. 20π mA leading by 90°
c. 10 mA leading by 90°
d. 10π mA lagging by 90°

22 Problem

In the figure shown, all elements used are ideal. For time t < 0, S1 remained
closed and S2 open. At t = 0, S1 is opened and S2 is closed. If the voltage Vc2
across the capacitor C2 at t = 0 is zero, the voltage across the capacitor
combination at t = 0+ will be

a. 1V
b. 2V
c. 1.5V
d. 3V

23 Problem

Transformer and emitter follower can both be used for impedance matching at
the output of an audio amplifier. The basic relationship between the input
power Pjn and output power Pout in both the cases is

a. Pin = Pout for both transformer and emitter follower
b. Pin > Pout for both transformer and emitter follower
c. Pin < Pout for transformer and Pjn = P0ut for emitter follower
d. Pin = Pout for transformer and Pjn < Pout for emitter follower

24 Problem

The equivalent capacitance of the input loop of the circuit shown is

a. 2 μF
b. 100 μF
c. 200 μF
d. 4 μF

25 Problem

In an 8085 microprocessor, the contents of the Accumulator, after the
following instructions are executed will become XRA A
MVIB FOH
SUB B
a. 01 H
b. OF H
c. F0 H
d. 10 H

26 Problem

For the Y-bus matrix of a 4-bus system given in per unit, the buses having shunt
elements are
YBUS = J

a. 3 and 4
b. 2 and 3
c. 1 and 2
d. 1, 2 and 4

27 Problem

The unit-step response of a unity feedback system with open loop transfer
function G(s) = K/((s + I) (s + 2)) is shown in the figure. The value of K is

a. 0.5
b. 2
c. 4
d. 6

28 Problem

The open loop transfer function of a unity feedback system is given by G (s) =
(e-0.1s)/ s. The gain margin of this system is

a. 11.95dB
b. 17.67dB
c. 21.33dB
d. 23.9dB

29 Problem

Match the items in List-I with the items in List-ll and select the correct answer
using the codes given below the lists.

List-I To List-ll Use
a improve power factor 1 shunt reactor
b reduce the current ripples 2 shunt capacitor
c increase the power flow in line 3 series capacitor
d reduce the Ferranti effect 4 series reactor

a. A 2, b 3, c 4, d 1
b. a 2, b 4, c 3, d 1
c. a 4, b 3, c 1, d 2
d. A 4, b 1, c 3, d 2

30 Problem

Match the items in List-I with the items in List-ll and select the correct answer
using the codes given below the lists.

List I List ll
Type of transmission line Type of distance relay
preferred
a Short Line 1 Ohm Relay
b Medium Line 2 Reactance Relay
c Long Line 3 Mho Relay

a. a 2, b 1, c 3,
b. a 3, b 2, c 1
c. a 1, b 2, c 3
d. a 1, b 3, c 2

31 Problem

Three generators are feeding a load of 100 MW. The details of the generators
are

Rating Efficiency Regulation (p.u.) on
(MW) (%) 100 MVA base
Generator-1 100 20 0.02
Generator-2 100 30 0.04
Generator -3 100 40 0.03
In the event of increased load power demand, which of the following will
happen?

a. All the generators will share equal power
b. Generator-3 will share more power compared to Generator-1
c. Generator-1 will share more power compared to Generator-2

32 Problem

A 500MW, 21 kV, 50Hz, 3-phase, 2-pole synchronous generator having a rated
p.f = 0.9, has a moment of inertia of 27.5 x 103 kg-m2. The inertia constant (H)
will be

a. 2.44s
b. 2.71s
c. 4.88s
d. 5.42s

33 Problem

f(x, y) is a continuous function defined over (x, y) Є [0, 1] × [0, 1], Given the
two constraints, x > y2 and y > x2, the volume under f(x, y) is

y 1 x y

a. f ( x, y )dxdy
y 0 x y 2

y 1 x 1

b. f ( x, y ) dxdy
2 2
y x x y

y 1 x 1

c. f ( x, y)dxdy
y 0 x 0

y xx y

d. f ( x, y )dxdy
y 0 x 0

34 Problem

Assume for simplicity that N people, all born in April (a month of 30 days), are
collected in a room. Consider the event of at least two people in the room
being born on the same date of the month, even if in different years, e.g. 1980
and 1985. What is the smallest N so that the probability of this event exceeds
0.5?

a. 20
b. 7
c. 15
d. 16

35 Problem

A cascade of 3 Linear Time Invariant systems is causal and unstable. From this,
we conclude that

a. Each system in the cascade is individually causal and unstable
b. At least one system is unstable and at least one system is causal
c. At least one system is causal and all systems are unstable
d. The majority are unstable and the majority are causal

36 Problem

The Fourier Series coefficient, of a periodic signal x(t), expressed as
x(t) = k ae
k
are given by
j 2 kt / T

A-2 = 2 - j1; a-1 = 0.5 + j0.2; a0 = j2; a1 = 0.5 - j0.2; a2 = 2 + j1; and
ak = 0; for |k| > 2. Which of the following is true?

a. x(t) has finite energy because only finitely many coefficients are non-zero
b. x(t) has zero average value because it is periodic
c. The imaginary part of x(t) is constant
d. The real part of x(t) is even

37 Problem

The z-transform of a signal x[n] is given by 4z-3 + 3z-1 + 2 - 6z2 + 2z3. It is applied
to a system, with a transfer function H (z) = 3z-1 - 2. Let the output be y(n).
Which of the following is true?

a. y(n) is non causal with finite support
b. y(n) is causal with infinite support
c. y(n) = 0; |n| > 3
d. Re [Y (z)]z = e = - Re [Y (z)] z= e ; lm [Y (z)]z= e =|m [Y (z)]z = e
j j j j ;-

38 Problem

A cubic polynomial with real coefficients

a. can possibly have no extrema and no zero crossings
b. may have up to three extrema and up to 2 zero crossings
c. cannot have more than two extrema and more than three zero crossings
d. will always have an equal number of extrema and zero crossings

39 Problem

Let x2 - 117 = 0. The iterative steps for the solution using Newton -Raphson's
method is given by

a. xk +1 = (1/2)(xk + (117/xk))
b. xk + 1 = xk - (117/xk)
c. xk +1 = xk - (xk/117)
d. xk + 1 = xk - (1/2) (xk + (117/xk))

40 Problem

F (x, y) = (x2 + xy) a x + (y2 + xy)a y. It's line integral over the straight line from (x,
ˆ ˆ

y) = (0, 2) to (x, y) = (2, 0) evaluates to

a. -8
b. 4
c. 8
d. 0

41 Problem

An ideal opamp circuit and its input waveform are shown in the figures. The
output waveform of this circuit will be

a. b.

c. d.

42 Problem

A 220V, 50Hz, single-phase induction motor has the following connection
diagram and winding orientations shown. MM' is the axis of the main stator
winding (M1M2) and AA' is that of the auxiliary winding (A1 A2). Directions of
the winding axes indicate direction of flux when currents in the windings are in
the directions shown. Parameters of each winding are indicated. When switch
S is closed, the motor

a. rotates clockwise
b. rotates anticlockwise
c. does not rotate
d. rotates momentarily and comes to a halt

43 Problem

The circuit shows an ideal diode connected to a pure inductor and is connected
to a purely sinusoidal 50Hz voltage source. Under ideal conditions the current
waveform through the inductor will look like

a. b.

c. d.

44 Problem

The Current Source Inverter shown in figure, is operated by alternately turning
on thyristor pairs (T1, T2) and (T3, T4). If the load is purely resistive, the
theoretical maximum output frequency obtainable will be

a. 125kHz
b. 250kHz
c. 500kHz
d. 50kHz

45 Problem

In the chopper circuit shown, the main thyristor (TM) is operated at a duty ratio
of 0.8, which is much larger the commutation interval. If the maximum
allowable reapplied dv/dt on TM is 50 V/μs, what should be the theoretical
minimum value of C1? Assume current ripple through L0 to be negligible.

a. 0.2 μF
b. 0.02 μF
c. 2 μF
d. 20 μF

46 Problem

Match the switch arrangements on the top row to the steady-state V-l
characteristics on the lower row. The steady state operating points are shown
by large black dots

a. A- I, B - II, C - III, D - IV
b. A - II, B - IV, C – I, C - III
c. A - IV, B - III, C - I, D - II
d. A – VI, B - III, C - II, D - I

47 Problem

For the circuit shown, find out the current flowing through the Ω resistance.
Also identify the changes to be made to double the current through the 20Ω
resistance

a. (5A; Put Vs = 20V)
b. (2A; Put Vs = 8V)
c. (5A; Put Is = 10A)
d. (7A; Put Is = 12A)

48 Problem

The figure shows a three-phase delta connected load supplied from a 400V, 50
Hz, 3-phase balanced source. The pressure coil (PC) and current coil (CC) of a
wattmeter are connected to the load as shown, with the coil polarities suitably
selected to ensure a positive deflection. The wattmeter reading will be

a. 0
b. 1600 Watt
c. 800 Watt
d. 400 Watt

49 Problem

An average-reading digital multimeter reads 10V when fed with a triangular
wave, symmetric about the time-axis. For the same input an rms-reading meter
will read.

a. 2 O/√3
b. 10/√3
c. 20√3
d. 10√3

50 Problem

Figure shows the extended view of a 2 pole dc machine with 10 armature
conductors. Normal brush positions are shown by A and B, placed at the
interpolar axis. If the brushes are now shifted, in the direction of rotation, to A'
and B' as shown, the voltage waveform VA'B' will resemble

a. b.

c. d.

The star- delta transformer shown above is excited on the star side with a
balanced , 4 –wire ,3 phase , sinusoidal voltage supply of rated magnitude . The
transformer is under no load condition.

51 Problem

With both S1 and S2 open, the core flux waveform will be

a. A sinusoid at fundamental frequency
b. Flat topped with third harmonic
c. Peaky with third harmonic
d. None of these

52 Problem

With S2 closed and S1 open, the current waveform in the delta winding will be

a. a sinusoid at fundamental frequency
b. flat topped with third harmonic
c. only third harmonic
d. None of these

The circuit diagram shows a two winding, lossless transformer with no leakage
Flux, excited from a current source, i(t) whose waveform is also shown The
transformer has a magnetizing inductance of 400/mh

53 Problem

The peak voltage across A and B, with S open is

a. 400/πV
b. 800V
c. 4000/πV
d. 800/πV

54 Problem

If the waveform of i(t) is changed to i (t) = 10 sin (100) A, the peak voltage

across A and B with S closed is

a. 400 V
b. 240V
c. 320 V
d. 160 V
A system is described by the following state and output equations
((dx1(t))/dt) = -3x1 (t)+x2 (t) + 2u (t)
((dx2(t))/dt) = - 2x2 (t) + u (t)
V (t) = X1(t)
where u (t) is the input and y (t) is the output

55 Problem

The system transfer function is

a. (s + 2)/(s2 + 5s - 6)
b. (s + 3)/(s2 + 5s + 6)
c. (s + 5)/(s2 + 5s + 6)
d. (2s - 5)/(s2 + 5s - 6)

56 Problem

The state transition matrix of the above system is

3t
e 0
a. 2t 3t 2t
e e e

3t 2t 3t
e e e
b. 0 e 2t

3t 2t 3t
e e e
c. 0 e 2t

e3t e 2t
e 3t

d. 0 e 2t

The figure above shows coils 1 and 2 with dot markings as shown , having
4000 and 6000 turns respectively. Both coils have a rated current of 25 A Coil
1 is excited with single phase, 400V, 50 Hz supply

57 Problem

The coils are to be connected to obtain a single phase, 400/1000V, auto
transformer to drive a load of 10kVA. Which of the options given should be
exercised to realize the required auto transformer?

a. Connect A and D; Common B
b. Connect B and D; Common C
c. Connect A and C; Common B
d. Connect A and C; Common D

58 Problem

In the autotransformer obtained in above Question, the current in each coil is

a. Coil-1 is 25 A and Coil-2 is 10 A
b. Coil-1 is 10 A and Coil-2 is 25 A
c. Coil-1 is 10 A and Coil-2 is 15 A
d. Coil-1 is 15 A and Coil-2 is 10 A

59 Problem

For the circuit given above, the Thevenin's resistance across the terminals A and
B is

a. 0.5kΩ
b. 0.2kΩ
c. 1 KΩ
d. 0.11k Ω

60 Problem

For the circuit given above, the Thevenin's voltage across the terminals A and B
is

a. 1.25V
b. 0.25V
c. 1V
d. 0.5V

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Electrical Engineering - 2009 Unsolved Paper

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