Gate ee 2009 with solutions

GATE EE
2009
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Q.1 - Q.20 carry one mark each.
MCQ 1.1 The pressure coil of a dynamometer type wattmeter is
(A) Highly inductive (B) Highly resistive
(C) Purely resistive (D) Purely inductive
SOL 1.1 Reading of wattmeter (Power) in the circuit
Pav
T
VIdt1 T
0
= =# Common are between V I−
total common area = 0 (Positive and negative area are equal)
So P 0av =
Hence (A) is correct option.
MCQ 1.2 The measurement system shown in the figure uses three sub-systems in cascade
whose gains are specified as , ,1/G G G1 2 3. The relative small errors associated with
each respective subsystem ,G G1 2 and G3 are ,1 2ε ε and 3ε . The error associated with
the output is :
(A) 1
1 2
3
ε ε
ε
+ + (B)
3
1 2
ε
ε ε
(C) 1 2 3ε ε ε+ − (D) 1 2 3ε ε ε+ +

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SOL 1.2 Overall gain of the system is written as
G G G
G
1
1 2
3
=
We know that for a quantity that is product of two or more quantities total
percentage error is some of the percentage error in each quantity. so error in overall
gain G is
G3 1
1 2
3
ε ε
ε
= + +
Hence (D) is correct option.
MCQ 1.3 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
SOL 1.3 Figure shows current characteristic of diode during switching.
MCQ 1.4 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

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(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
SOL 1.4 A circle is produced when there is a 90c phase difference between vertical and
horizontal inputs.
MCQ 1.5 The increasing order of speed of data access for the following device is
(I) Cache Memory
(II) CD-ROM
(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)
SOL 1.5 The increasing order of speed is as following
Magnetic tape> CD-ROM> Dynamic RAM>Cache Memory>Processor register
Hence (B) is correct option.
MCQ 1.6 A field excitation of 20 A in a certain alternator results in an armature current
of 400 A in short circuit and a terminal voltage of 2000 V on open circuit. The
magnitude of the internal voltage drop within the machine at a load current of 200
A is
(A) 1 V (B) 10 V
(C) 100 V (D) 1000 V
SOL 1.6 Hence (D) is correct option.
Given field excitation of 20 A=
Armature current 400 A=
Short circuit and terminal voltage 200 V=
On open circuit, load current 200 A=
So, Internal resistance 5
400
2000 Ω= =
Internal vol. drop 5 200#=
1000 V=
MCQ 1.7 The current through the 2 kΩ resistance in the circuit shown is

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(A) 0 mA (B) 1 mA
(C) 2 mA (D) 6 mA
SOL 1.7 Hence (A) is correct option
In the bridge
R R1 4 1R R2 3= =
So it is a balanced bridge
I 0= mA
MCQ 1.8 Out of the following plant categories
(i) Nuclear
(ii) Run-of-river
(iii) Pump Storage
(iv) Diesel
The base load power plant are
(A) (i) and (ii) (B) (ii) and (iii)
(C) (i), (ii) and (iv) (D) (i), (iii) and (iv)
SOL 1.8 Hence ( ) is correct Option
MCQ 1.9 For a fixed value of complex power flow in a transmission line having a sending end
voltage V , the real loss will be proportional to
(A) V (B) V 2
(C)
V
1
2
(D)
V
1

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SOL 1.9 Hence (C) is correct option.
We know complex power
S ( )cos sinP jQ VI jφ φ= + = +
VIej
= φ
I
Ve
S
j= φ
a Real Power loss I R2
=
PL
Ve
S R
e
S R
V
1
j j
2
2
2
2#= =φ φc m e
S R Constantj2
2
a =φ
So PL
V
1
2
MCQ 1.10 How many 200 W/220 V incandescent lamps connected in series would consume
the same total power as a single 100 W/220 V incandescent lamp ?
(A) not possible (B) 4
(C) 3 (D) 2
SOL 1.10 Resistance of the bulb rated 200 W/220 V is
R1
P
V
1
2
=
( )
242
200
220 2
Ω= =
Resistance of 100 W/220 V lamp is
RT
P
V
2
2
=
( )
484
100
220 2
Ω= =
To connect in series
RT n R1#=
484 242n #=
n 2=
Hence (D) is correct option
MCQ 1.11 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 τ− is applied to a system with
impulse response ( )h t τ− , the output will be
(A) ( )y τ (B) ( ( ))y t2 τ−
(C) ( )y t τ− (D) ( )y t 2τ−
Let ( ) ( )x t X s
L
( ) ( )y t Y s
L
( ) ( )h t H s
L
So output of the system is given as

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( )Y s ( ) ( )X s H s=
Now for input ( )x t τ− ( )e X s (shifting property)sL τ-
( )h t τ− ( )e H ssL τ−
So now output is '( )Y s ( ) ( )e X s e H ss s
$= τ τ- -
'( )Y s ( ) ( )e X s H ss2
= τ-
'( )Y s ( )e Y ss2
= τ-
Or '( )y t ( 2 )y t τ= −
MCQ 1.12 The nature of feedback in the op-amp circuit shown is
(A) Current-Current feedback (B) Voltage-Voltage feedback
(C) Current-Voltage feedback (D) Voltage-Current feedback
SOL 1.12 Equivalent circuit of given amplifier
Feedback samples output voltage and adds a negative feedback voltage ( )vfb to
input.
So, it is a voltage-voltage feedback.
MCQ 1.13 The complete set of only those Logic Gates designated as Universal Gates is
(A) NOT, OR and AND Gates
(B) XNOR, NOR and NAND Gates
(C) NOR and NAND Gates
(D) XOR, NOR and NAND Gates

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SOL 1.13 NOR and NAND gates considered as universal gates.
Hence (C) is correct Option
MCQ 1.14 The single phase, 50 Hz iron core transformer in the circuit has both the vertical
arms of cross sectional area 20 cm2
and both the horizontal arms of cross sectional
area 10 cm2
. 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
SOL 1.14 Given single-phase iron core transformer has both the vertical arms of cross section
area 20 cm2
, and both the horizontal arms of cross section are 10 cm2
So, Inductance NBA
1
= (proportional to cross section area)
When cross section became half, inductance became half.
Hence (C) is correct option.
MCQ 1.15 A3-phasesquirrelcageinductionmotorsuppliedfromabalanced3-phasesourcedrivesa
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
SOL 1.15 Given 3-phase squirrel cage induction motor.

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At point A if speed -, Torque -
speed ., Torque .
So A is stable.
At point B if speed - Load torque .
So B is un-stable.
MCQ 1.16 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.
SOL 1.16 SCR has the property that it can be turned ON but not OFF with a gate pulse, So
SCR is being considered to be a semi-controlled device.
MCQ 1.17 The polar plot of an open loop stable system is shown below. The closed loop
system is
(A) always stable
(B) marginally stable
(C) un-stable with one pole on the RH s-plane
(D) un-stable with two poles on the RH s-plane
SOL 1.17 From Nyquist stability criteria, no. of closed loop poles in right half of s-plane is
given as
Z P N= −
P " No. of open loop poles in right half s-plane
N " No. of encirclement of ( 1, 0)j−

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Here N 2=− (` encirclement is in clockwise direction)
P 0= (` system is stable)
So, ( )Z 0 2= − −
Z 2= , System is unstable with 2-poles on RH of s-plane.
MCQ 1.18 The first two rows of Routh’s tabulation of a third order equation are as follows.
s
s
2
4
2
4
3
2
This means there are
(A) Two roots at s j!= and one root in right half s-plane
(B) Two roots at 2s j!= and one root in left half s-plane
(C) Two roots at 2s j!= and one root in right half s-plane
(D) Two roots at s j!= and one root in left half s-plane
SOL 1.18 Given Routh’s tabulation.
s3
2 2
s2
4 4
s1
0 0
So the auxiliary equation is given by,
s4 42
+ 0=
s2
1=−
s j!=
From table we have characteristic equation as
s s s2 2 4 43 2
+ + + 0=
s s s2 23 2
+ + + 0=
( ) ( )s s s1 2 12 2
+ + + 0=
( )( )s s2 12
+ + 0=
s 2=− , s j!=
MCQ 1.19 The asymptotic approximation of the log-magnitude v/s frequency plot of a system
containing only real poles and zeros is shown. Its transfer function is

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(A)
( )( )
( )
s s s
s
2 25
10 5
+ +
+
(B)
( )( )
( )
s s s
s
2 25
1000 5
2
+ +
+
(C)
( )( )
( )
s s s
s
2 25
100 5
+ +
+
(D)
( )( )
( )
s s s
s
2 25
80 5
2
+ +
+
SOL 1.19 Since initial slope of the bode plot is 40− dB/decade, so no. of poles at origin is 2.
Transfer function can be written in following steps:
Slope changes from 40− dB/dec. to 60− dB/dec. at 21ω = rad/sec., so at 1ω there
is a pole in the transfer function.
Slope changes from 60− dB/dec to 40− dB/dec at 52ω = rad/sec., so at this
frequency there is a zero lying in the system function.
The slope changes from 40− dB/dec to 60− dB/dec at 253ω = rad/sec, so there
is a pole in the system at this frequency.
Transfer function
( )T s
( )( )
( )
s s s
K s
2 25
5
2=
+ +
+
Constant term can be obtained as.
( )T j .at 0 1
ω ω =
80=
So, 80
( . )
( )
log
K
20
0 1 50
5
2
#
=
K 1000=
therefore, the transfer function is
( )T s
( )( )
( )
s s s
s
2 25
1000 5
2=
+ +
+
MCQ 1.20 The trace and determinant of a 2 2# matrix are known to be 2− and 35−
respectively. Its eigenvalues are
(A) 30− and 5− (B) 37− and 1−
(C) 7− and 5 (D) 17.5 and 2−
Let the matrix is A
a
c
b
d
= > H

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Trace of a square matrix is sum of its diagonal entries
Trace A a d= + 2=−
Determinent ad bc− 35=−
Eigenvalue A Iλ− 0=
a
c
b
d
λ
λ
−
−
0=
( )( )a d bcλ λ− − − 0=
( ) ( )a d ad bc2
λ λ− + + − 0=
( ) ( )2 352
λ λ− − + − 0=
2 352
λ λ+ − 0=
( )( )5 7λ λ− + 0=
,1 2λ λ ,5 7= −
Q.21 to Q.60 carry two marks each.
MCQ 1.21 The following circuit has 10 , 10R Ck FμΩ= = . The input voltage is a sinusoidal
at 50 Hz with an rms value of 10 V. Under ideal conditions, the current Is
from
the source is
(A) 10π mA leading by 90%
(B) 20π mA leading by 90%
(C) 10π mA leading by 90%
(D) 10π mA lagging by 90%
SOL 1.21 Let voltages at positive and negative terminals of op-amp areV+ andV- respectively,
then
V V Vs= =+ - (ideal op-amp)
In the circuit we have,
( )
Cs
V
R
V V s
1
0 0− +
−- -
` j
0=
( ) ( )RCs V V V s0+ −- - 0=
(1 )RCs Vs+ ( )V s0=

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Similarly current Is is,
Is
R
V Vs 0
= −
Is
R
RCs Vs=
Is j CVsω=
Is CV 90s +ω= + %
Is f2 10 10 106
# # #π= -
Is 2 50 10 10 106
# # # # #π= -
Is 10π= mA, leading by 90%
MCQ 1.22 In the figure shown, all elements used are ideal. For time ,t S0< 1 remained closed
and S2 open. At ,t S0 1= 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) 1 V (B) 2 V
(C) 1.5 V (D) 3 V
SOL 1.22 For 0t < , S1 is closed and S2 is opened so the capacitor C1 will charged upto 3 volt.
(0)VC1 3= Volt
Now when switch positions are changed, by applying charge conservation
(0 )C Veq C1
+
(0 ) (0 )C V C VC C1 21 2
= ++ +
(2 1) 3#+ 1 3 2 (0 )VC2# #= + +
9 3 2 (0 )VC2
= + +
(0 )VC2
+
3= Volt
MCQ 1.23 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 Pin
and output power Pout
in both the cases is
(A) P Pin out= for both transformer and emitter follower
(B) P P>in out for both transformer and emitter follower
(C) P P<in out for transformer and P Pin out= for emitter follower
(D) P Pin out= for transformer and P P<in out for emitter follower
SOL 1.23 Input and output power of a transformer is same

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P Pin out=
for emitter follower, )voltage gain(Av 1=
( )Acurrent gain i 1>
( )PPower out A A Pv i in=
Since emitter follower has a high current gain so P P>out in
MCQ 1.24 The equivalent capacitance of the input loop of the circuit shown is
(A) 2 Fμ (B) 100 Fμ
(C) 200 Fμ (D) 4 Fμ
SOL 1.24 Hence (A) is correct option.
Applying KVL in the input loop
(1 1) 10 ( 49 )v i
j C
i i1
1 1
3
1 1# ω
− + − + 0=
v1 2 10 50i
j C
i13
1 1# ω
= +
Input impedance
Z1
i
v
1
1
=
2 10
( / )j C 50
13
#
ω
= +
So, equivalent capacitance
Ceq
C
50
= 2
F
F
50
100 n
n= =
MCQ 1.25 In an 8085 microprocessor, the contents of the Accumulator, after the following
instructions are executed will become
XRA A

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MVI B, F0 H
SUB B
(A) 01 H (B) 0F H
(C) F0 H (D) 10 H
SOL 1.25 For the given instruction set,
XRA A& XOR A with A & A = 0
MVI B, F0 H&B F0 H=
SUB B &A A B= −
A 0 0 0 0 0 0 0 0=
B 11 1 0 0 0 01=
2’s complement of ( )B− 0 0 01 0 0 0 0=
( )A B A B+ − = − 0 0 01 0 0 0 0=
10 H=
MCQ 1.26 For the Y-bus matrix of a 4-bus system given in per unit, the buses having shunt
elements are
. .
.
.
Y j
5
2
2 5
0
2
10
2 5
4
2 5
2 5
9
4
0
4
4
8
BUS =
−
−
−
−
R
T
S
S
S
S
S
V
X
W
W
W
W
W
(A) 3 and 4 (B) 2 and 3
(C) 1 and 2 (D) 1, 2 and 4
SOL 1.26 YBus matrix of Y-Bus system are given as
YBus
. .
.
.
j
5
2
2 5
0
2
10
2 5
4
2 5
2 5
9
4
0
0
4
8
=
−
−
−
−
R
T
S
S
S
S
SS
V
X
W
W
W
W
WW
We have to find out the buses having shunt element
We know YBus
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
11
21
31
41
12
22
32
42
13
23
33
43
14
24
34
44
=
R
T
S
S
S
S
SS
V
X
W
W
W
W
WW
Here
y11 y y y y j510 12 13 14= + + + =−
y22 y y y y j1020 21 23 24= + + + =−

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y33 y y y y j930 31 32 34= + + + =−
y44 y y y y j840 41 42 43= + + + =−
y12 y y j221 12= =− =
y13 .y y j2 531 13= =− =
y14 y y j041 14= =− =
y23 .y y j2 532 23= =− =
y24 y y j442 24= =− =
So
y10 5 2 2.5 0 0.5y y y y j j j j j11 12 13 14= − − − =− + + + =−
y20 . .y y y y j j j j j10 2 2 5 4 1 522 12 23 24= − − − =− + + + =−
y30 . .y y y y j j j j9 2 5 2 5 4 033 31 32 34= − − − =− + + + =
y40 y y y y j j j8 0 4 4 044 41 42 43= − − − =− − + + =
Admittance diagram is being made by as
From figure. it is cleared that branch (1) & (2) behaves like shunt element.
MCQ 1.27 The unit-step response of a unity feed back system with open loop transfer function
( ) /(( 1)( 2))G s K s s= + + is shown in the figure.
The value of K is
(A) 0.5 (B) 2
(C) 4 (D) 6
SOL 1.27 From the figure we can see that steady state error for given system is
ess . .1 0 75 0 25= − =

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Steady state error for unity feed back system is given by
ess
1 ( )
( )
lim
G s
sR s
s 0
=
+"
= G
( )( )
lim
s s
K
s
1
1 2
s
s
0
1
=
+
+ +
"
^ h
> H
; ( )R s
s
1= (unit step input)
1
1
K
2
=
+
K2
2=
+
So, ess 0.25
K2
2=
+
=
2 0.5 0.25K= +
K
.
.
0 25
1 5 6= =
MCQ 1.28 Theopenlooptransferfunctionofaunityfeedbacksystemisgivenby ( ) ( )/G s e s. s0 1
= -
. The gain margin of the is system is
(A) 11.95 dB (B) 17.67 dB
(C) 21.33 dB (D) 23.9 dB
SOL 1.28 Open loop transfer function of the figure is given by,
( )G s
s
e . s0 1
=
−
( )G jω
j
e .j0 1
ω
=
ω−
Phase cross over frequency can be calculated as,
( )G j p+ ω 180c=−
0.1 180 90p # cω
π
− −b l 180c=−
.0 1 180
p #
cω
π
90c=
.0 1 pω
180
90 #
c
c π=
pω .15 7= rad/sec
So the gain margin (dB)
( )
log
G j
20 1
pω
= e o
.
log20
15 7
1
1=
b l> H
.log20 15 7=
.23 9= dB

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MCQ 1.29 Match the items in List-I (To) with the items in the List-II (Use) and select the
correct answer using the codes given below the lists.
List-I
a. improve power factor
b. reduce the current ripples
c. increase the power flow in line
d. reduce the Ferranti effect
List-II
1. shunt reactor
2. shunt capacitor
3. series capacitor
4. series reactor
(A) 2, 3, 4, 1a b c d" " " "
(B) 2, 4, 3, 1a b c d" " " "
(C) 4, 3, 1, 2a b c d" " " "
(D) a 4, b 1, c 3, d 2" " " "
SOL 1.29 We know that
• Shunt Capacitors are used for improving power factor.
• Series Reactors are used to reduce the current ripples.
• For increasing the power flow in line we use series capacitor.
• Shunt reactors are used to reduce the Ferranti effect.
Hence (B) is correct option
MCQ 1.30 Match the items in List-I (Type of transmission line) with the items in List-II
(Type of distance relay preferred) and select the correct answer using the codes
given below the lists.
List-I
a. Short Line
b. Medium Line
c. Long Line
List-II
1. Ohm Relay
2. Reactance Relay
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" " "
SOL 1.30 We know that for different type of transmission line different type of distance relays
are used which are as follows.
Short Transmission line -Ohm reactance used
Medium Transmission Line -Reactance relay is used
Long Transmission line -Mho relay is used
MCQ 1.31 Three generators are feeding a load of 100 MW. The details of the generators are

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Rating
(MW)
Efﬁciency
(%)
Regulation (Pu.)
( on 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 generator 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
(D) Generator-2 will share more power compared to Generator-3
SOL 1.31 Given that three generators are feeding a load of 100 MW. For increased load
power demand, Generator having better regulation share More power, so Generator
-1 will share More power than Generator -2.
MCQ 1.32 A 500 MW, 21 kV, 50 Hz, 3-phase, 2-pole synchronous generator having a rated p.f
= 0.9, has a moment of inertia of 27.5 103
# kg-m2
.The inertia constant (H ) will be
(A) 2.44 s (B) 2.71 s
(C) 4.88 s (D) 5.42 s
SOL 1.32 Given Synchronous generator of 500 MW, 21 kV, 50 Hz, 3-φ, 2-pole
0.9P.F = , Moment of inertia 27.5 10M 3
#= kg-m2
Inertia constant H ?=
Generator rating in MVA G
.
500 555.56
cos
P
0 9
MW MVA
φ
= = =
N 3000
2
120 50
pole
120 f# #= = = rpm
Stored K.E
2
2
1
2
1
60
M M N2
2
ω π= = b l
27.5 10
2
1
60
2 3000 MJ3
# # # #π= b l
1357.07 MJ=
Inertia constant ( )H
Rating of Generator (MVA)
Stored K.E=
H
.
.
555 56
1357 07=
2.44 sec=
MCQ 1.33 ( , )f x y is a continuous function defined over ( , ) [ , ] [ , ]x y 0 1 0 1#! . Given the two
constraints, x y> 2
and y x> 2
, the volume under ( , )f x y is
(A) ( , )f x y dxdy
x y
x y
y
y
0
1
2
=
=
=
=
## (B) ( , )f x y dxdy
x y
x
y x
y 11
22
=
=
=
=
##

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(C) ( , )f x y dxdy
x
x
y
y
0
1
0
1
=
=
=
=
## (D) ( , )f x y dxdy
x
x y
y
y x
00 =
=
=
=
##
SOL 1.33 Given constraints x y> 2
and y x> 2
h
Limit of y : y 0= to y 1=
Limit of x :x y2
= to x y x y2
&= =
So volume under ( , )f x y
V ( , )f x y dx dy
x y
x y
y
y
0
1
2
=
=
=
=
=
##
Hence (A) is correct option
MCQ 1.34 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
SOL 1.34 No of events of at least two people in the room being born on same date Cn
2=
three people in the room being born on same date Cn
3=
similarly four for people Cn
4=
probabilty of the event, 0.5
N
C C C C N 7
n n n n
n2 3 4
&$ $ g$ =
Hence(B) is correct option.
MCQ 1.35 A cascade of three 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 on 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

PUBLISHING FOR GATE
SOL 1.35 Let three LTI systems having response ( ), ( )H z H z1 2 and ( )H z3 are
Cascaded as showing below
Assume ( )H z1 1z z2 1
= + + (non-causal)
( )H z2 1z z3 2
= + + (non-causal)
Overall response of the system
( )H z ( ) ( ) ( )H z H z H z1 2 3=
( )H z ( )( ) ( )z z z z H z1 12 1 3 2
3= + + + +
To make ( )H z causal we have to take ( )H z3 also causal.
Let ( )H z3 z z 16 4
= + +- -
( )H z ( )( )( )z z z z z z1 1 12 1 3 2 6 4
= + + + + + +- -
( )H z causal"
Similarly to make ( )H z unstable atleast one of the system should be unstable.
MCQ 1.36 The Fourier Series coefficients of a periodic signal ( )x t expressed as
( )x t a e /
k
j kt T
k
2
= 3
3 π
=-
/ are given by 2 1a j2 = −- , 0.5 0.2a j1 = +− , a j20 = ,
. .a j0 5 0 21 = − , a j2 12 = + and a 0k = 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
SOL 1.36 Given signal
( )x t a e /
k
j kt T
k
2
=
3
3
π
=-
/
Let 0ω is the fundamental frequency of signal ( )x t
( )x t a ek
jk t
k
0
=
3
3
ω
=-
/
T
2
0a π ω=
( )x t a e a e a a e a ej t j t j t j t
2
2
1 0 1 2
20 0 0 0
= + + + +ω ω ω ω
-
-
-
-
(2 ) (0.5 0.2 ) 2j e j e jj t j t2 0 0
= − + + + +ω ω- -
(0.5 0.2) (2 )e j ej t j t20 0
+ − + +ω ω
2 e e j e ej t j t j t j t2 2 2 20 0 0 0
= + + − +ω ω ω ω- -
6 6@ @
0.5 0.2 2e e j e e jj t j t j t j t0 0 0 0
+ − − +ω ω ω ω- + -
6 6@ @

PUBLISHING FOR GATE
2(2 2 ) (2 2 ) 0.5(2 )cos sin cost j j t t0 0 0ω ω ω= + + −0.2 (2 ) 2sinj j t j0ω +
[4 2 2 2cos sin cost t t0 0 0ω ω ω= − + +0.4 ] 2sin t j0ω +
[ ( )]Im x t 2 (constant)=
MCQ 1.37 The z-transform of a signal [ ]x n is given by z z z z4 3 2 6 23 1 2 3
+ + − +- -
It is applied to a system, with a transfer function ( )H z z3 21
= −-
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 n0 3>=
(D)
[ ( )] [ ( )]
[ ( )] [ ( )] ;
Re Re
Im Im
Y z Y z
Y z Y z <
z e z e
z e z e
j j
j j #π θ π
=−
= −
= =
= =
i i
i i
-
-
SOL 1.37 Z-transform of [ ]x n is
( )X z z z z z4 3 2 6 23 1 2 3
= + + − +- -
Transfer function of the system
( )H z z3 21
= −-
Output
( )Y z ( ) ( )H z X z=
( )Y z (3 2)(4 3 2 6 2 )z z z z z1 3 1 2 3
= − + + − +- - -
z z z z z z z12 9 6 18 6 8 64 2 1 2 3 1
= + + − + − −- - - - -
4 12 4z z2 3
− + −
z z z z z z12 8 9 4 18 18 44 3 2 2 3
= − + − − + −- - -
Or sequence [ ]y n is
[ ]y n [ ] [ ] [ ] [ ]n n n n12 4 8 3 9 2 4δ δ δ δ= − − − + − − −
18 [ 1] 18 [ 2] 4 [ 3]n n nδ δ δ+ + + − +
[ ]y n 0=Y , 0n <
So [ ]y n is non-causal with finite support.
MCQ 1.38 A cubic polynomial with real coefficients
(A) Can possibly have no extrema and no zero crossings
(B) May have up to three extrema and upto 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
SOL 1.38 Assume a Cubic polynomial with real Coefficients
( )P x a x a x a x a0
3
1
3
2 3= + + +
, , ,a a a a0 1 2 3 are real
'( )P x a x a x a3 20
2
1 2= + +

PUBLISHING FOR GATE
''( )P x a x a6 20 1= +
'''( )P x 6a0=
( )P xiv
0=
Hence (C) is correct Option
MCQ 1.39 Let x 117 02
− = . The iterative steps for the solution using Newton-Raphon’s
method is given by
(A) x x
x2
1 117
k k
k
1 = ++ b l (B) x x
x
117
k k
k
1 = −+
(C) x x x
117k k
k
1 = −+ (D) x x x
x2
1 117
k k k
k
1 = − ++ b l
SOL 1.39 An iterative sequence in Newton-Raphson’s method is obtained by following
expression
xk 1+
'( )
( )
x
f x
f x
k
k
k
= −
( )f x x 1172
= −
'( )f x x2=
So ( )f xk x 117k
2
= −
'( )f xk x2 2 117k #= =
So xk 1+
117x
x
x
2k
k
k
2
= − −
x x
x2
1 117
k k
k
= − +: D
MCQ 1.40 ( , ) ( ) ( )x y x xy y xyF a ax y
2 2
= + + +t t . It’s line integral over the straight line from
( , ) ( , )x y 0 2= to ( , ) ( , )x y 2 0= evaluates to
(A) 8− (B) 4
(C) 8 (D) 0
SOL 1.40 Equation of straight line
y 2− ( )x
2 0
0 2 0=
−
− −
y 2− x=−
F dl$ [( ) ( ) ][ ]x xy y xy dx dy dza a a a ax y x y z
2 2
= + + + + +t t t t t
( ) ( )x xy dx y xy dy2 2
= + + +
Limit of x : 0 to 2
Limit of y : 2 to 0
F dl$# ( ) ( )x xy dx y xy dy2 2
2
0
0
2
= + + +##

PUBLISHING FOR GATE
Line y 2− x=−
dy dx=−
So F dl$# [ ( )] ( )x x x dx y y y dy2 22
0
2 2
2
0
= + − + + −# #
xdx y dy2 2
2
0
0
2
= + ##
x y
2
2
2
2
2
0
2 2
2
0
= +: ;D E
4 4= −
0=
MCQ 1.41 An ideal op-amp circuit and its input wave form as shown in the figures. The
output waveform of this circuit will be

PUBLISHING FOR GATE
SOL 1.41 This is a schmitt trigger circuit, output can takes two states only.
V 6OH =+ volt
3VOL =− volt
Threshold voltages at non-inverting terminals of op-amp is given as
V V
2
6
1
0TH TH− + − 0=
3 6VTH − 0=
VTH 2= V (Upper threshold)
Similarly
( )V V
2
3
1
TL TL− −
+ 0=
3 3VTL + 0=
VTL 1=− V (Lower threshold)
For 2V Volt,<in 6V Volt0 =+
2V Volt,>in 3V Volt0 =−
1V Volt<in − 6V Volt0 =+
1V Volt>in − 3V Volt0 =−
Output waveform
Hence(D) is correct option.
MCQ 1.42 A 200 V, 50 Hz, single-phase induction motor has the following connection diagram
and winding orientations as shown. MM’ is the axis of the main stator winding
(M M )1 2 and AA’ is that of the auxiliary winding(A A )1 2 . Directions of the winding
axis 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

PUBLISHING FOR GATE
(A) rotates clockwise
(B) rotates anti-clockwise
(C) does not rotate
(D) rotates momentarily and comes to a halt
MCQ 1.43 The circuit shows an ideal diode connected to a pure inductor and is connected
to a purely sinusoidal 50 Hz voltage source. Under ideal conditions the current
waveform through the inductor will look like.

PUBLISHING FOR GATE
Current wave form for iL
vL
dt
LdiL
=
iL v dt
2
1
L= #
for 0 < t +ω π, vL 10sinv t
dt
diL
in ω= = =
iL 100cosv dt t C
2
1
L π= =− +#
at /t100 2π π= , iL 0= , C 0=
iL cos t100 π=−
i (L peak) 1 Amp= for t<π ω 0v vL in= =

PUBLISHING FOR GATE
MCQ 1.44 The Current Source Inverter shown in figure is operated by alternately turning on
thyristor pairs (T ,T )1 2 and (T ,T )3 4 . If the load is purely resistive, the theoretical
maximum output frequency obtainable will be
(A) 125 kHz (B) 250 kHz
(C) 500 kHz (D) 50 kHz
SOL 1.44 In CSI let T3 and T4 already conducting at t 0=
At triggering T1 and T2, T3 and T4 are force commulated.
Again at t T
2
= , T1 and T2 are force commutated. This completes a cycle.
Time constant τ . secRC 4 0 5 2# μ= = =
frequency f 5001
2 10
1
6
#τ
= = =− kHz

PUBLISHING FOR GATE
MCQ 1.45 In the chopper circuit shown, the main thyristor (T )M 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/ sμ , what should be the theoretical minimum value
of C1 ? Assume current ripple through L0 to be negligible.
(A) 0.2 Fμ (B) 0.02 Fμ
(C) 2 Fμ (D) 20 Fμ
duty ratio TM .0 8=
maximum
dt
dv on TM 50 V/ secμ=
minimum value of C1 ?=
Given that current ripple through L0 is negligible.
current through TM I duty ratio currentm #= =
0.8 12.5 10 A#= =
a Im C
dt
dv
1=
10 C
10
50
1 6#= −
C1 10 0.2
10
50 F6
# μ= =−
MCQ 1.46 Match the switch arrangements on the top row to the steady-state
V -I characteristics on the lower row. The steady state operating points are shown
by large black dots.

PUBLISHING FOR GATE
(A) P-I, Q-II, R-III, S-IV (B) P-II, Q-IV, R-I, S-III
(C) P-IV, Q-III, R-I, S-II (D) P-IV, Q-III, R-II, S-I
SOL 1.46 Characteristics are as
Hence (C) is correct option
MCQ 1.47 For the circuit shown, find out the current flowing through the 2 Ω resistance. Also
identify the changes to be made to double the current through the 2 Ω resistance.

PUBLISHING FOR GATE
(A) (5 ; 30 )VA Put VS = (B) (2 ; 8 )VA Put VS =
(C) (5 ; 10 )IA Put AS = (D) (7 ; 12 )IA Put AS =
SOL 1.47 Voltage across 2 X resistor, VS 2= V
Current, I2Ω
V
2
S
=
2
4 2= = A
To make the current double we have to take
VS 8= V
MCQ 1.48 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
Wattmeter reading P V IPC CC=
VPC " Voltage across potential coil.
ICC " Current in current coil.
VPC 400 120Vbc c+= = −
ICC 4 120I
100
400 120
ac
c c+ += = =
Power P 400 120 4 120#c c+ += −
1600 240c+=
1600
2
1
#=
800= Watt
MCQ 1.49 An average-reading digital multi-meter reads 10 V when fed with a triangular wave,

PUBLISHING FOR GATE
symmetric about the time-axis. For the same input an rms-reading meter will read
(A)
3
20 (B)
3
10
(C) 20 3 (D) 10 3
Average value of a triangular wave Vav
V
3
m
=
rms value Vms
V
3
m
=
Given that Vav
V
3
10m
= = V
So Vrms
V V
3
3 10 3m
av= = = V
MCQ 1.50 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 V ' 'A B will resemble

PUBLISHING FOR GATE
SOL 1.50 Wave form VA Bl l
Common Data Questions
Common Data for Questions 51 and 52:
The star-delta transformer shown above is excited on the star side with balanced,
4-wire, 3-phase, sinusoidal voltage supply of rated magnitude. The transformer is
under no load condition
MCQ 1.51 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

PUBLISHING FOR GATE
SOL 1.51 When both S1 and S2 open, star connection consists 3rd
harmonics in line current
due to hysteresis A saturation.
MCQ 1.52 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
SOL 1.52 Since S2 closed and S1 open, so it will be open delta connection and output will be
sinusoidal at fundamental frequency.
Common Data for Questions 53 and 54 :
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 π mH.
MCQ 1.53 The peak voltage across A and B, with S open is
(A) 400
π
V (B) 800 V
(C) 4000
π
V (D) 800
π
V
SOL 1.53 Peak voltage across A and B with S open is
V ( )m
dt
di m slope of I t#= = −

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10400
5 10
10 8003
3# #
#π π
= =−
−: D V
MCQ 1.54 If the wave form of ( )i t is changed to ( ) 10 (100 )sini t tπ= A, the peak voltage
across A and B with S closed is
(A) 400 V (B) 240 V
(C) 320 V (D) 160 V
Common Data for Question 55 and 56 :
A system is described by the following state and output equations
( )
( ) ( ) ( )
( )
2 ( ) ( )
( ) ( )
dt
dx t
x t x t u t
dt
dx t
x t u t
y t x t
3 21
1 2
2
2
1
=− + +
=− +
=
when ( )u t is the input and ( )y t is the output
MCQ 1.55 The system transfer function is
(A)
s s
s
5 6
2
2
+ −
+ (B)
s s
s
5 6
3
2
+ +
+
(C)
s s
s
5 6
2 5
2
+ +
+ (D)
s s
s
5 6
2 5
2
+ −
−
SOL 1.55 Given system equations
( )
dt
dx t1
3 ( ) ( ) 2 ( )x t x t u t1 2=− + +
( )
dt
dx t2
( ) ( )x t u t2 2=− +
( )y t ( )x t1=
Taking Laplace transform on both sides of equations.
( )sX s1 ( ) ( ) ( )X s X s U s3 21 2=− + +
( ) ( )s X s3 1+ ( ) ( )X s U s22= + ...(1)
Similarly
( )sX s2 ( ) ( )X s U s2 2=− +
( ) ( )s X s2 2+ ( )U s= ...(2)
From equation (1) & (2)
( ) ( )s X s3 1+
( )
( )
s
U s
U s
2
2=
+
+
( )X s1
( ) ( )
s
U s
s
s
3 2
1 2 2
=
+ +
+ +
; E

PUBLISHING FOR GATE
( )X s1 ( )
( )( )
( )
U s
s s
s
2 3
2 5
=
+ +
+
From output equation,
( )Y s ( )X s1=
So, ( )Y s ( )
( )( )
( )
U s
s s
s
2 3
2 5
=
+ +
+
System transfer function
( )
( )
U s
Y s
T.F =
( )( )
( )
s s
s
2 3
2 5
=
+ +
+
( )
s s
s
5 6
2 5
2=
+ +
+
MCQ 1.56 The state-transition matrix of the above system is
(A)
e
e e e
0t
t t t
3
2 3 2
+
-
- - -= G (B)
e e e
e0
t t t
t
3 2 3
2
−- - -
-= G
(C)
e e e
e0
t t t
t
3 2 3
2
+- - -
-= G (D)
e e e
e0
t t t
t
3 2 3
2
−- -
-= G
SOL 1.56 Given state equations in matrix form can be written as,
x
x
1
2
o
o> H ( )
x
x
tu
3
0
1
2
2
1
1
2
=
−
−
+> > >H H H
( )
dt
d tX
( ) ( )A t B tX u= +
State transition matrix is given by
( )tφ ( )sL 1
Φ= −
6 @
( )sΦ ( )sI A 1
= − −
( )sI A−
s
s0
0 3
0
1
2
= −
−
−> >H H
( )sI A−
s
s
3
0
1
2
=
+ −
+> H
( )sI A 1
− −
( )( )s s
s
s3 2
1 2
0
1
3
=
+ +
+
+> H
So ( ) ( )s sI A 1
Φ = − − ( ) ( )( )
( )
s s s
s
3
1
3 2
1
2
1=
+ + +
+0
R
T
S
S
S
SS
V
X
W
W
W
WW
( ) [ ( )]t sL 1
φ Φ= − e e e
e0
t t t
t
3 2 3
2=
−− − −
−> H

PUBLISHING FOR GATE
Statement for Linked Answer Questions 57 and 58 :
The figure above shows coils-1 and 2, with dot markings as shown, having 4000
and 6000 turns respectively. Both the coils have a rated current of 25 A. Coil-1 is
excited with single phase, 400 V, 50 Hz supply.
MCQ 1.57 The coils are to be connected to obtain a single-phase, 1000
400
V,
auto-transformer to drive a load of 10 kVA. 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
N1 4000=
N2 6000=
I 25 A=
V 400 V= , 50f Hz=
Coil are to be connected to obtain a single Phase,
1000
400 V auto transfer to drive
Load 10 kVA
Connected A & D common B
MCQ 1.58 In the autotransformer obtained in Question 16, the current in each coil is
(A) Coil-1 is 25 A and Coil-2 is 10 A

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(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
SOL 1.58 Given 3-phase, 400 V, 5 kW, Star connected synchronous motor.
Internal Resistance 10 Ω=
Operating at 50% Load, unity p.f.
So
kVA rating 25 400#=
1000=
Internal Resistance 10 Ω=
So
kVA rating 1000 10#=
10000 kVA=
Statement for Linked Answer Question 59 and 60 :
MCQ 1.59 For the circuit given above, the Thevenin’s resistance across the terminals A and
B is
(A) 0.5 kΩ (B) 0.2 kΩ
(C) 1 kΩ (D) 0.11 kΩ
SOL 1.59 To obtain equivalent thevenin circuit, put a test source between terminals AB
By applying KCL at super node
V V V
2
5
2 1
P P S− + + IS=
5 2V V VP P S− + + 2IS=

PUBLISHING FOR GATE
2 2V VP S+ 2 5Is= +
V VP S+ 2.5IS= + ...(1)
V VP S− 3VS=
& VP 4VS=
So, 4V VS S+ 2.5IS= +
5VS 2.5IS= +
VS 0.2 0.5IS= + ...(2)
For thevenin equivalent circuit
VS I R VS th th= +
...(3)
By comparing (2) and (3),
Thevenin resistance Rth 0.2 kΩ=
MCQ 1.60 For the circuit given above, the Thevenin’s voltage across the terminals A and B is
(A) 1.25 V (B) 0.25 V
(C) 1 V (D) 0.5 V
SOL 1.60 Hence (D) is correct option
From aboveVth 0.5= V
.
Answer Sheet
1. (A) 13. (C) 25. (D) 37. (A) 49. (D)
2. (D) 14. (C) 26. (C) 38. (C) 50. (A)
3. (A) 15. (A) 27. (D) 39. (D) 51. (B)
4. (D) 16. (C) 28. (D) 40. (D) 52. (A)
5. (B) 17. (D) 29. (B) 41. (D) 53. (D)
6. (D) 18. (D) 30. (C) 42. (*) 54. (*)
7. (A) 19. (B) 31. (C) 43. (D) 55. (C)
8. (*) 20. (C) 32. (A) 44. (C) 56. (B)
9. (C) 21. (A) 33. (A) 45. (A) 57. (A)
10. (D) 22. (D) 34. (B) 46. (C) 58. (D)
11. (D) 23. (D) 35. (B) 47. (B) 59. (B)
12. (B) 24. (A) 36. (C) 48. (C) 60. (D)

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