Intelli Electronic and Communication Technical evaluation

Electronic and Communication – Sample Paper - Technical evaluation – ECE

1) An AM signal is detected using an envelope detector The carrier frequency and

modulating signal frequency are 1 MHz and 2 kHz respectively. An appropriate value for

the time constant of the envelope detector is

A) 500 msec

B) 20 msec

C) 0.2 msec

D) 1 msec

Answer: (B)

2) In a PCM system, if the code word length is increased from 6 to 8 bits, the signal to

quantization noise ratio improves by the factor

A) 8/6

B) 12

C) 16

D) 8

Answer: (C)

3) Consider the following statements S1 and S2.

S1: The b of a bipolar transistor reduces if the base width is increased.

S2: The b of a bipolar transistor increases if the doping concentration in the base is

increased. Which one of the following is correct?

A) S1 is FALSE and S2 is TRUE

B) Both S1 and S2 are TRUE

C) Both S1 and S2 are FALSE

D) S1 is TRUE and S2 is FALSE

Answer: (D)

4) In relation to the synchronous machines, which one of the following statements is false?

A) In salient pole machines, the direct-axis synchronous reactance is greater than the

quadrature-axis synchronous reactance

B) The damper bars help the synchronous motor self start

C) Short circuit ratio is the ratio of the field current required to produce the rated voltage on

open circuit to the rated armature current

D) The V-curve of a synchronous motor represents the variation in the armature current with

field excitation, at a given output power

Answer : (C)

5) A parallel plate air-filled capacitor has plate area of l0-4 m2 and plate separation of 10-3

m. It is connected to a 0.5 V, 3.6 GHz source. The magnitude of the displacement current

is (e0 = 1/36p x 10-9 F/m)

A) 10 mA

B) 100 mA

C) 10 A

D) 1.59 mA

Answer: (A)

6) In a PCM system, if the code word length is increased from 6 to 8 bits, the signal to

quantization noise ratio improves by the factor

A) 8/6

B) 12

C) 16

D) 8

Answer: (C)

7) At an industrial sub-station with a 4 MW load, a capacitor of 2 MVAR is installed to

maintain the load power factor at 0.97 lagging. If the capacitor goes out of serivce, the

load power factor becomes

A) 0.85

B) 1.00

C) 0.80 lag

D) 0.90 lag

Answer : (C)

8) The conduction loss versus device current characteristic of a power MOSFET is best

approximated by

A) a parabola

B) a straight line

C) a rectangular hyperbola

D) an exponentially decaying function

Answer : (A)

9) The drain of an n-channel MOSFET is shorted to the gate so that VGS = VDS. The

threshold voltage (VT) of MOSFET is 1 V. If the drain current (ID) is 1 mA for VGS = 2V, then

for VGS = 3V, ID is

A) 2 mA

B) 3 mA

C) 9 mA

D) 4 mA

Answer: (D)

10) For the polynomial P(s) = s5 + s4 + 2s3 + 2s2 + 3s + 15, the number of roots which lie in

the right half of the s-plane is

A) 4

B) 2

C) 3

D) 1

Answer : (B)