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Delhi University Entrance Test (DUET) 2020 Previous Year Question Paper With Answer Key

DU PhD in Electronics
Topic: ELEC PHD S2
1) The complex number
can be expressed in
form as follows
[Question ID = 5438]
1.
[Option ID = 21746]
2.
[Option ID = 21747]
3.
[Option ID = 21748]
4.
[Option ID = 21749]
Correct Answer :
[Option ID = 21748]
2)
[Question ID = 5439]
1.
[Option ID = 21750]
2.
[Option ID = 21751]
3.
[Option ID = 21752]
4.
[Option ID = 21753]
Correct Answer :
[Option ID = 21753]
3)
[Question ID = 5440]
1.
[Option ID = 21754]
2.
[Option ID = 21755]
3.
[Option ID = 21756]
4.
[Option ID = 21757]
Correct Answer :

---

[Option ID = 21756]
4) For the given differential equation,
The general solution of this equation will be
[Question ID = 5441]
1.
[Option ID = 21758]
2.
[Option ID = 21759]
3.
[Option ID = 21760]
4.
[Option ID = 21761]
Correct Answer :
[Option ID = 21759]
5) Given
where t is a parameter and c is a constant, then
in terms of t only is
[Question ID = 5442]
1.
[Option ID = 21762]
2.
[Option ID = 21763]
3.
[Option ID = 21764]
4.
[Option ID = 21765]
Correct Answer :
[Option ID = 21762]
6)
The eigen values of the matrix
are
[Question ID = 5443]
1. 2,3,6
[Option ID = 21766]
2. 2,3,6
[Option ID = 21767]
3. 2,3,6
[Option ID = 21768]
4. 2,3,6
[Option ID = 21769]
Correct Answer :
2,3,6
[Option ID = 21768]

---

7) For which value of will the given matrix become singular?
[Question ID = 5444]
1. 1
[Option ID = 21770]
2. 0
[Option ID = 21771]
3. 4
[Option ID = 21772]
4. 2
[Option ID = 21773]
Correct Answer :
4
[Option ID = 21772]
8)
If A is orthogonal matrix and
, the values of a and b are
[Question ID = 5445]
1.
[Option ID = 21774]
2.
[Option ID = 21775]
3.
[Option ID = 21776]
4.
[Option ID = 21777]
Correct Answer :
[Option ID = 21774]
9) The particular solution for
is
[Question ID = 5446]
1.
[Option ID = 21778]
2.
[Option ID = 21779]
3.
[Option ID = 21780]
4.
[Option ID = 21781]
Correct Answer :
[Option ID = 21778]

---

10) The partial differentiation equation
can be classified as
[Question ID = 5447]
1. parabolic
[Option ID = 21782]
2. hyperbolic
[Option ID = 21783]
3. none of these
[Option ID = 21784]
4. elliptic
[Option ID = 21785]
Correct Answer :
elliptic
[Option ID = 21785]
11)
[Question ID = 5448]
1. 0.66 [Option ID = 21786]
2. 0.44 [Option ID = 21787]
3. 0.88 [Option ID = 21788]
4. 0.22 [Option ID = 21789]
Correct Answer :
0.88 [Option ID = 21788]
12) The velocity v(in kilometre/minute) of a motorbike which starts from rest, is given at fixed intervals of time t(in
minutes) as follows:
t
2
4
6
8
10
12
14
16
18
20
v
10
18
25
29
32
20
11
5
2
0
The approximate distance (in kilometres) rounded to two places of decimals covered in 20 minutes using Simpson's
1/3rd rule is
[Question ID = 5449]
1. 200
[Option ID = 21790]
2. 309
[Option ID = 21791]
3. 119
[Option ID = 21792]
4. 234
[Option ID = 21793]
Correct Answer :
309
[Option ID = 21791]
13) Consider
with all real coefficients. It is known that its derivative p'(s) has no real
roots. The number of real roots of p(s) is
[Question ID = 5450]
1. 0
[Option ID = 21794]
2. 1
[Option ID = 21795]
3. 2
[Option ID = 21796]
4. 3
[Option ID = 21797]

---

Correct Answer :
1
[Option ID = 21795]
14) Gauss Seidel method is used to solve the following equations (as per the given order):
x + 2x
1
+ 3x
2
= 5;
3
2x + 3x
1
+ x
2
= 1;
3
3x + 2x
1
+ x
2
= 3;
3
Assuming initial guess as x =x
1
=x
2
=0, the value of x
3
after the first iteration is
3
[Question ID = 5451]
1. 1.55
[Option ID = 21798]
2. 2.55
[Option ID = 21799]
3. 1.00
[Option ID = 21800]
4. 3.67
[Option ID = 21801]
Correct Answer :
1.55
[Option ID = 21798]
15) The function f(x)=ex ? 1 is to be solved using NewtonRaphson method, an initial guess of x is taken as 1.0, then the
0
absolute error observed at 2n iteration is
d
[Question ID = 5452]
1. 0.50 [Option ID = 21802]
2. 1.25 [Option ID = 21803]
3. 0.25 [Option ID = 21804]
4. 0.33 [Option ID = 21805]
Correct Answer :
0.25 [Option ID = 21804]
16) IF
is the Fourier transform of
then the Fourier transform of
is
[Question ID = 5453]
1.
[Option ID = 21806]
2.
[Option ID = 21807]
3.
[Option ID = 21808]
4.
[Option ID = 21809]
Correct Answer :
[Option ID = 21808]
17) The Fourier cosine transform of
is
[Question ID = 5454]
1.
[Option ID = 21810]
2.

---

[Option ID = 21811]
3.
[Option ID = 21812]
4.
[Option ID = 21813]
Correct Answer :
[Option ID = 21811]
18) Using Laplace transform evaluate the given integral

[Question ID = 5455]
1.
[Option ID = 21814]
2. 1
[Option ID = 21815]
3.
[Option ID = 21816]
4. 0
[Option ID = 21817]
Correct Answer :
[Option ID = 21814]
19)
[Question ID = 5456]
1.
[Option ID = 21818]
2.
[Option ID = 21819]
3.
[Option ID = 21820]
4.
[Option ID = 21821]
Correct Answer :
[Option ID = 21819]

---

20) The inverse Laplace transform of
is
[Question ID = 5457]
1.
[Option ID = 21822]
2.
[Option ID = 21823]
3.
[Option ID = 21824]
4.
[Option ID = 21825]
Correct Answer :
[Option ID = 21825]
21) Which MATLAB command will return the corner elements of a 5by5 matrix A?
[Question ID = 5458]
1. A([1,1], [end, end]) [Option ID = 21826]
2. A({[1,1], [1, end], [end,1], [end, end]}) [Option ID = 21827]
3. A(1:end, 1:end) [Option ID = 21828]
4. A([1, end], [1, end]) [Option ID = 21829]
Correct Answer :
A([1, end], [1, end]) [Option ID = 21829]
22) Two vectors created in MATLAB as
>> X = [7 7 7 7];
>> Y=6:9;
The output of the command X == Y is
[Question ID = 5459]
1. 0 1 0 0
[Option ID = 21830]
2. 6 7 8 9
[Option ID = 21831]
3. 7 7 7 7
[Option ID = 21832]
4. 0 1 0 1
[Option ID = 21833]
Correct Answer :
0 1 0 0
[Option ID = 21830]
23) Consider the following MATLAB vectors:
x = [ 1 2 ];
y = [ 3 4 ];
z = [ x' [ y ; y ] ]';
What is the value of z after this program executes?
[Question ID = 5460]
1.
[Option ID = 21834]

---

2.
[Option ID = 21835]
3.
[Option ID = 21836]
4.
[Option ID = 21837]
Correct Answer :
[Option ID = 21837]
24) In C language, what is the output of the following code?
int main()
{
int j = 4;
printf("%d%d",j,j++);
}
[Question ID = 5461]
1. 44
[Option ID = 21838]
2. 45
[Option ID = 21839]
3. 54
[Option ID = 21840]
4. 55
[Option ID = 21841]
Correct Answer :
54
[Option ID = 21840]
25) In C language, what is the output of the following code?
int main()
{
int a=52;
printf("%o %x",a,a);
}
[Question ID = 5462]
1. 052 0x52
[Option ID = 21842]
2. 64 34
[Option ID = 21843]
3. 62 43
[Option ID = 21844]
4. error
[Option ID = 21845]
Correct Answer :
64 34
[Option ID = 21843]
26) The length and cross sectional area of ntype photo conductor are 150 ?m and 10 cm
7
respectively. What is the
2

---

electron transit time at an applied voltage of 15 V? (Assume mobility of electron ?
2
n = 950 cm /V.s)
[Question ID = 5463]
1. 15.8 ns
[Option ID = 21846]
2. 10.5 ns
[Option ID = 21847]
3. 7.4 ns
[Option ID = 21848]
4. 3.1 ns
[Option ID = 21849]
Correct Answer :
15.8 ns
[Option ID = 21846]
27) If the number density of a free electron gas changes from 10 to 10
27
electrons/m
25
then the value of plasma
3
frequency (in Hz) changes from 9.85 ? 10 to _______________
14
[Question ID = 5464]
1. 9.85 ? 10
10 [Option ID = 21850]
2. 9.85 ? 10
9 [Option ID = 21851]
3. 9.85 ? 10
13 [Option ID = 21852]
4. 9.85 ? 10
7 [Option ID = 21853]
Correct Answer :
9.85 ? 10
13 [Option ID = 21852]
28) Match List I with List II typical spectroscopic regions type of transitions

List I
List II
I. Electron transition involving valance
A. Infrared region
electrons
B. Ultraviolet visible
II. Nuclear transitions
region
C. Xray region
III. Vibrational transitions of molecules
D. ray region
IV. Transitions involving inner shell electrons
Choose the correct answer from the options given below:

[Question ID = 5465]
1. A III, B I, C IV, D II
[Option ID = 21854]
2. A IV, B II, C I, D III
[Option ID = 21855]
3. A I, B II, C III, D IV
[Option ID = 21856]
4. A III, B IV, C I, D II
[Option ID = 21857]
Correct Answer :
A III, B I, C IV, D II
[Option ID = 21854]
29) The value of at which the first order peak in Xray ( = 1.53 ?) diffraction corresponding to (1 1 1) plane of a single
cubic structure with the lattice constant a = 2.65 ? is proximately
[Question ID = 5466]
1. 15?
[Option ID = 21858]
2. 45?
[Option ID = 21859]
3. 30?
[Option ID = 21860]
4. 90?

---

[Option ID = 21861]
Correct Answer :
30?
[Option ID = 21860]
30) If an IMPATT diode amplifier has negative resistance Rd = 15 and load resistance R = 25 the power gain is
L
[Question ID = 5467]
1. 25 [Option ID = 21862]
2. 0 [Option ID = 21863]
3.
[Option ID = 21864]
4. 16 [Option ID = 21865]
Correct Answer :
16 [Option ID = 21865]
31) How many AND gates are required for 1 to 16 demultiplexer?
[Question ID = 5468]
1. 8 [Option ID = 21866]
2. 16 [Option ID = 21867]
3. 14 [Option ID = 21868]
4. 20 [Option ID = 21869]
Correct Answer :
16 [Option ID = 21867]
32) A 12 bit ADC is used to convert analog voltage of 0 to 10 V into digital. The resolution is
[Question ID = 5469]
1. 24.4 mV
[Option ID = 21870]
2. 2.44 mV
[Option ID = 21871]
3. 1.2 V
[Option ID = 21872]
4. none of these
[Option ID = 21873]
Correct Answer :
2.44 mV
[Option ID = 21871]
33) The value of x for the given system:
= 6 is
[Question ID = 5470]
1. 17
[Option ID = 21874]
2. 15
[Option ID = 21875]
3. 16
[Option ID = 21876]
4. none of these
[Option ID = 21877]
Correct Answer :
17
[Option ID = 21874]
34) The input impedance of the following circuit

---

[Question ID = 5471]
1. 120 k [Option ID = 21878]
2. 110 k [Option ID = 21879]
3. 10 k [Option ID = 21880]
4. Infinity [Option ID = 21881]
Correct Answer :
10 k [Option ID = 21880]
35) What is the bandwidth of single stage amplifier if its rise time is 0.35 microseconds?
[Question ID = 5472]
1. 2 MHz [Option ID = 21882]
2. 5 KHz [Option ID = 21883]
3. 1 MHz [Option ID = 21884]
4. 2 KHz [Option ID = 21885]
Correct Answer :
1 MHz [Option ID = 21884]
36) If the electric field strength E of an electromagnetic wave in free space is given by E = 2cos wtz/no ay V/m. The
magnetic flux density B is calculated as
[Question ID = 5473]
1.
[Option ID = 21886]
2.
[Option ID = 21887]
3.
[Option ID = 21888]
4.
[Option ID = 21889]
Correct Answer :
[Option ID = 21886]
37) The electric field acting on an electron (charge 1.6 x 1019 C) which is 1 m away from a perfectly conducting plane
[Question ID = 5474]
1. 181 V/m
[Option ID = 21890]
2. 360 V/m
[Option ID = 21891]
3. 543 V/m
[Option ID = 21892]
4. 271 V/m
[Option ID = 21893]
Correct Answer :
360 V/m
[Option ID = 21891]
38) An electron starts with zero velocity from a cathode which is at a potential of 5 kV and then moves into a region
where the potential is zero. The velocity of this electron is
[Question ID = 5475]
1. 32.65 ? 10 m/s
6
[Option ID = 21894]
2. 31.55 ? 10 m/s
7
[Option ID = 21895]
3. 41.95 ? 10 m/s
6
[Option ID = 21896]
4. 52.65 ? 10 m/s
7
[Option ID = 21897]
Correct Answer :

---

41.95 ? 10 m/s
6
[Option ID = 21896]
39) A power generator whose source impedance is 50 W is connected to an oscilloscope by 1 m of 75 W polythene (er=2.5)
filled coaxial cable. The VSWR and phase velocity of the waves on the cable, respectively are
[Question ID = 5476]
1. 2.0 and 0.70 ? 10 m/s
8
[Option ID = 21898]
2. 1.3 and 3.65 ? 10 m/s
8
[Option ID = 21899]
3. 1.5 and 1.90 ? 10 m/s
8
[Option ID = 21900]
4. 2.5 and 2.50 ? 10 m/s
7
[Option ID = 21901]
Correct Answer :
1.5 and 1.90 ? 10 m/s
8
[Option ID = 21900]
40) A transmission line is terminated by a resistance load which is less than the characteristic impedance and VSWR on the
line is 1.5. The ratio of reflected wave to the incident wave in decibels is
[Question ID = 5477]
1. 0 dB [Option ID = 21902]
2. 1.5 Db [Option ID = 21903]
3. 13.98 dB [Option ID = 21904]
4. 1.5 dB [Option ID = 21905]
Correct Answer :
13.98 dB [Option ID = 21904]
41) The power internally generated within a doublehetero junction LED if it has internal quantum efficiency of 54.5 % and
drive current of 50 mA with a peak emission wavelength of 0.72 m is
[Question ID = 5478]
1. 0.09 W [Option ID = 21906]
2. 0.047 W [Option ID = 21907]
3. 0.01 W [Option ID = 21908]
4. 0.6 W [Option ID = 21909]
Correct Answer :
0.047 W [Option ID = 21907]
42) For a phototransistor having gain of 116.5, wavelength of 1.28 m, optical power 123W. The collector current is
[Question ID = 5479]
1. 7.46 mA [Option ID = 21910]
2. 1.23 mA [Option ID = 21911]
3. 5.24 mA [Option ID = 21912]
4. 14.76 mA [Option ID = 21913]
Correct Answer :
14.76 mA [Option ID = 21913]
43) In 8086 microprocessor the overflow flag is set when
[Question ID = 5480]
1. the sum is more than 16 bits [Option ID = 21914]
2. carry and sign flags are set. [Option ID = 21915]
3. Subtraction [Option ID = 21916]
4. signed numbers go out of their range after an arithmetic operation [Option ID = 21917]
Correct Answer :
signed numbers go out of their range after an arithmetic operation [Option ID = 21917]
44) What is the bit size of the 8051 microcontroller?
[Question ID = 5481]
1. 4 bit [Option ID = 21918]
2. 16 bit [Option ID = 21919]
3. 128 bit [Option ID = 21920]
4. 8 bit [Option ID = 21921]
Correct Answer :
8 bit [Option ID = 21921]
45) A 50 lossless transmission line has a pure reactance of j100 as its load. The VSWR in the line is
[Question ID = 5482]
1. (infinity)
[Option ID = 21922]
2. (half)
[Option ID = 21923]

---

3. 4 (four)
[Option ID = 21924]
4. 2 (two)
[Option ID = 21925]
Correct Answer :
(infinity)
[Option ID = 21922]
46) The bit stream 01001 is differentially encoded using `Delay and EXOR' scheme for DPSK transmission. Assuming the
reference bit as `1' and assigning phases of `0' and for 1's and 0's respectively in the encoded sequence, the
transmitted phase sequence becomes
[Question ID = 5483]
1. 00
[Option ID = 21926]
2. 00
[Option ID = 21927]
3. 000
[Option ID = 21928]
4. 0
[Option ID = 21929]
Correct Answer :
00
[Option ID = 21926]
47) An AM modulator has output xc(t) = Acos(400t)+ Bcos(380t)+ Bcos(420t). The carrier power is 100W and the
efficiency is 40%. The value of A and B are
[Question ID = 5484]
1. 14.14, 8.16
[Option ID = 21930]
2. 50, 10
[Option ID = 21931]
3. 22.36, 13.46
[Option ID = 21932]
4. None of these
[Option ID = 21933]
Correct Answer :
14.14, 8.16
[Option ID = 21930]
48) To prevent overloading of the last IF amplifier in a receiver, one should use
[Question ID = 5485]
1. Squelch [Option ID = 21934]
2. Variable sensitivity [Option ID = 21935]
3. Variable selectivity [Option ID = 21936]
4. Double conversion [Option ID = 21937]
Correct Answer :
Variable sensitivity [Option ID = 21935]
49) A base band PCM system with a matched filter at receiver is implemented with ?5V bipolar pulse with pulse duration of
72?sec. If the noise power spectral density is 1.0 x 104 V /Hz, the probability of error for this system is given by
2
[Question ID = 5486]
1. 1.15 x 10
5 [Option ID = 21938]
2. 1.85 x 10
5 [Option ID = 21939]
3. 2.8 x 105 [Option ID = 21940]
4. 2.36 x 10
5 [Option ID = 21941]
Correct Answer :
1.15 x 10
5 [Option ID = 21938]
50) Eight base band analog signals each of 100 Hz bandwidth are to be transmitted by a signal binary PCM system in such a

---

way that the quantization error for each signal does not exceed 0.1% of the peak amplitude of the signal. The sampling rate
for each signal is to be 50% higher than its Nyquist rate. The bit transmission rate is
[Question ID = 5487]
1. 6 kbps [Option ID = 21942]
2. 26.4 kbps [Option ID = 21943]
3. 18 kbps [Option ID = 21944]
4. 24 kbps [Option ID = 21945]
Correct Answer :
26.4 kbps [Option ID = 21943]

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