# Online Electronics and Communication Engineering Test - Previous Exam Papers Test 4

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Instruction:

• This is a FREE online test. DO NOT pay money to anyone to attend this test.
• Total number of questions : 20.
• Time alloted : 30 minutes.
• Each question carry 1 mark, no negative marks.
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• All the best :-).

1.

A MOSFET has a threshold voltage of 1 V and oxide thickness of 500 x 10-8r = 3.9; ε0 = 8.85 x 10-14 F/cm, q = 1.6 x 10-19 c]. The region under the gate is ion implanted for threshold voltage tailoring. The base and type of impant required to shift threshold voltage to - 1 V are __________ .

A.
 8.6 x 1011/cm2, p-type
B.
 8.6 x 1011/cm2, n-type
C.
 0.86 x 109/cm2, p-type
D.
 1.02 x 1012/cm2, n-type

Your Answer: Option (Not Answered)

Correct Answer: Option A

Explanation:

VT(new) = VT(odd) +

= 6.903 x 10-8

fB = - 8.6 x 1011

The threshold voltage is always negative for p-channel and hence implant is of p-type.

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2.

Consider the following

1. Maximum energy of electrons liberated photoelectrically is independent of light intensity
2. Maximum energy of electrons liberated photoelectrically varies nonlinearly with frequency of incident light.

A.
 (1) is true and (2) is false
B.
 (1) and (2) both are true
C.
 (1) is false and (2) is true
D.
 (1) and (2) both are false

Your Answer: Option (Not Answered)

Correct Answer: Option A

Explanation:

Statement (ii) is false because maximum energy of photons varies linearly with frequency of incident light. It can be shown as follows :

F1 > F2 > F3

j = light intensity = constant

Photocurrent Vs Anode voltage with frequency and incident light as a parameter.

The light intensity is constant.

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3.

Given digits 2, 2, 3, 3, 3, 4, 4, 4, 4 how many distinct 4 digit numbers greater than 3000 can be formed?

A.
 50
B.
 51
C.
 52
D.
 54

Your Answer: Option (Not Answered)

Correct Answer: Option B

Explanation:

The given digits are 2, 2, 3, 3, 3, 4, 4, 4, 4 we have to find the numbers that are greater than 300

The first digit can be 3 or 4 but not 2.

Now, let us fix the first, second and third digits as 3, 2, 2, then the fourth place can be filled in 3 ways.

The number of ways is 3 similarly, we fix first third and fourth place as 3, 2 and 2 respectively (4) so the second place can be filled in 3 ways again,

The number of ways is 3

Now, we fix first, second and fourth, previous cases and we obtain the same result.

The number of ways is 3 so, the total number of ways is 9 similarly this can done by fixing the numbers as 3 and 4 (instead of 2) and thereby we obtain the a ways each

The number of numbers starting with 3 is 27

Similarly by taking 4 as the first digit we get 27 numbers

The number of numbers that are greater than 3000 is 27 + 27 = 54

But, 3222, 4222, is not possible as there are only two 2's, 3333 is not possible as there are only three 3's

The total number of numbers that are greater than 3000 is 54 - 3 = 51.

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4.

The number of variables in a function is odd and the number of minterms with even number of 0's are same as the number of minterms with odd number at 1 's, the expression formed can be represented in __________ as well as __________ form.

A.
 exclusive - OR, NOR
B.
 equivalence, exclusive - OR
C.
 AND, coincidence
D.
 OR, exclusive - OR

Your Answer: Option (Not Answered)

Correct Answer: Option B

Explanation:

With odd number of variables (n) terms with even number of 0's and terms with odd number of 1 's are the same.

Thus the k-map for the above condition with minterms represented by terms with even number of 0's is

for n = 3

The expression can be represented by equivalence (EX NOR) or (EX OR) expressions.

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5.

Find the power absorbed or delivered by each source:

A.
 a = -32 b = - 12 c = -80 d = -60
B.
 a = -32 b = - 12 c = 80 d = 60
C.
 a = 32 b = 12 c = -80 d = 60
D.
 a = -32 b = 12 c = 80 d = -60

Your Answer: Option (Not Answered)

Correct Answer: Option D

Explanation:

Source a : Power : 8 x (4) = - 32 W. Source A has delivered the power as it is. - ve.

Source b: Source B has absorbed power of + 12 W as power is positive

Source c: Source C has absorbed power of 5 x 16 = 80 W

Source d: Delivers power of 3 x ix x (5) = 3 x 4 x (- 5) = -60 W

Total power of the network is - 32 + 12 + 80 - 60 = 0 Watts.

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6.

For the network shown below, if VD = 12 V and VGSQ = - 2 V value of RS will be

A.
 13.35 kΩ
B.
 3.35 kΩ
C.
 33.31 kΩ
D.
 3.95 kΩ

Your Answer: Option (Not Answered)

Correct Answer: Option B

Explanation:

VGS = VG - IDRS

- 2 = 5.44 - 2.22 X 10-3 X RS

RS = 3.35 KΩ.

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7.

In the circuit shown, all the transmission line sections are lossless. The Voltage Standing Wave Ration (VSWR) on the 60W line is

A.
 1
B.
 1.64
C.
 2.5
D.
 3

Your Answer: Option (Not Answered)

Correct Answer: Option B

Explanation:

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8.

A parallel plate capacitor has surface density of rs C/m2. The dielectric inside capacitor is air. The electric field intensities outside and inside the capacitor are

A.
B.
C.
D.

Your Answer: Option (Not Answered)

Correct Answer: Option D

Explanation:

In case of capacitor, the charges on two plates of capacitor are of opposite sign.

We know that electric field due to infinite sheet charge with density rs is

Outside the capacitor, electric field intensities due to upper plate and lower plate cancel each other.

Eoutside = 0

Inside the capacitor, the electric field intensities due to upper and lower plate add together

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9.

One of a loss-less transmission line having the characteristic impedance of 75 Ω and length of 1cm is short-circuit. At 3 GHz, the input impedance at the other end of the transmission line is

A.
 0
B.
 resistive
C.
 capacitance
D.
 inductive

Your Answer: Option (Not Answered)

Correct Answer: Option D

Explanation:

X = 10 cm, ZL = 0, βl =

Thus Zin is Z0which is inductive.

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10.

If for certain x(t), the Fourier transform is:

Then for x(2t) the Fourier transform will be:

A.
B.
C.
D.
 same as X(jω)

Your Answer: Option (Not Answered)

Correct Answer: Option A

Explanation:

Using scaling property

.

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11.

Total electric field intensity is given as (V/m). The maximum value of will occur; if and only if

A.
B.
C.
D.

Your Answer: Option (Not Answered)

Correct Answer: Option B

Explanation:

To find value of y at which E will be maximum, differentiable ET with respect to y and set it equal to zero.

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12.

Which of the following algorithms design techniques is used in quick sort algorithm?

A.
 Dynamic programming
B.
 Backtracking
C.
 Divide and conquer
D.
 Greedy

Your Answer: Option (Not Answered)

Correct Answer: Option C

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13.

For a message signal m(t) = cos (2pfmt) and the carrier frequency fc, which of the following represents a single side band (SSB) signal?

A.
 cos (2pfmt) cos (2pfct)
B.
 cos (2pfct)
C.
 cos [2p(fc + fm) t]
D.
 [1 + cos (2pfmt) cos (2pfct)]

Your Answer: Option (Not Answered)

Correct Answer: Option C

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14.

The cross section of a JFET is shown in the following figure. Let Va be - 2 V and let Vp be the initial pinch-off voltage. If the width W is doubled (with other geometrical parameters and doping levels remaining the same), then the ratio between the mutual transconductances of the initial and the modified JFET is

A.
 4
B.
C.
D.

Your Answer: Option (Not Answered)

Correct Answer: Option C

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15.

Which one of the following is a regulated power supply?

A.
 IC 555
B.
 IC 844
C.
 IC 3080
D.
 IC 723

Your Answer: Option (Not Answered)

Correct Answer: Option D

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16.

Which of the following materials in not an insulator?

A.
 Diamond
B.
 Graphite
C.
 Bakelite
D.
 Lucite

Your Answer: Option (Not Answered)

Correct Answer: Option B

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17.

Consider the following statements regarding registers and latches:

1. Registers are made of edge-triggered FFs, whereas latches are made from level-triggered FFs.
2. Registers are temporary storage devices whereas latches are not.
3. A latch employs cross-coupled feedback connections.
4. A register stores a binary word whereas a latch does not.
Which of the above statements is/are correct?

A.
 1 only
B.
 1 and 3
C.
 2 and 3
D.
 3 and 4

Your Answer: Option (Not Answered)

Correct Answer: Option B

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18.

Which are of the following oscillators is well suited for the generation of wide range audio-frequency sine waves?

A.
 RC phase-shift oscillator
B.
 Wien-bridge oscillator
C.
 Colpitts oscillator
D.
 Hartley oscillator

Your Answer: Option (Not Answered)

Correct Answer: Option B

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19.

Which of the following is/are correct statement(s)?

1. Bus is a group of wires carrying information.
2. Bus is needed to achieve reasonable speed of operation.
3. Bus can carry data or address.
4. A bus can be shared by more than one device.
Select the correct answer from the codes given below

A.
 1 only
B.
 1 and 2 only
C.
 2, 3 and 4 only
D.
 1, 2, 3 and 4

Your Answer: Option (Not Answered)

Correct Answer: Option D

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20.

The input to a binary communication system, denoted by a random variable x, takes on one of the two values 0 or 1 with probabilities and . The behaviour of the communication system is modelled by
P(Y = 1 |x = 1|) = and P(Y = 0|x = 0) =
Find P(Y = 1)

A.
B.
C.
 1
D.

Your Answer: Option (Not Answered)

Correct Answer: Option B

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