15-05-2013, 12:25 PM
Electronics & Communication Model Question paper
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1 A digital-to-analog converter with a full-scale output voltage of 3.5 V has a
resolution close to 14m V. Its bit size is
A) 4
B) 8
C) 16
D) 32
Answer : (B)
2 A single-phase half-controlled rectifier is driving a separately excited dc motor.
The dc motor has a back emf constant of 0.5 V/rpm. The armature current is 5 A
without any ripple. The armature resistance is 2W. The converter is working from a
280 V, single phase ac source with a firing angle of 80°. Under this operating
condition, the speed of the motor will be
A) 339 rpm
B) 359 rpm
C) 366 rpm
D) 386 rpm
Answer : ©
3 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 : ©
4 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)
5 The 8085 assembly language instruction that stores the content of H and L
registers into the memory locations 2050H and 2051H, respectively, is
A) SPHL 2050H
B) SPHL2051H
C) SHLD 2050H
D) STAX 2050H
Answer : ©
6 If E is the electric field intensity, Ñ(Ñ x E ) is equal to
A) E
B) | E |
C) null vector
D) zero
Answer : (D)
7 The insulation strength of an EHV transmission line is mainly governed by
A) load power factor
B) switching over-voltages
C) harmonics
D) corona
Answer : (B)
8 The Q - meter works on the principle of
A) mutual inductance
B) self inductance
C) series resonance
D) parallel resonance
Answer : ©
9 A 800 kV transmission line is having per phase line inductance of 1.1 mH/km and
per phase line capacitance of 11.68 nF/km. Ignoring the length of the line, its ideal
power transfer capability in MW is
A) 1204 MW
B) 1504 MW
C) 2085 MW
D) 2606 MW
Answer : ©
10 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 : ©
11 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 : ©