Legal Metrology • Paper-III
In a three-phase semi-conductor, if firing angle is less than or equal to 60 degrees, then the duration of conduction of each thyristor and diode would be respectively
A)
60 degrees and 60 degrees
B)
90 degrees and 300
C)
120 degrees and 120 degrees
D)
180 degrees and 180 degrees
Correct option: C — 120 degrees and 120 degrees. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
The switching speed of ECL is very high, because the transistors
A)
are switched between cut-off and saturation regions
B)
and switches between active and saturation regions
C)
and switches between active and cut-off regions
D)
may operate in any of three regions
ECL has low voltage swing, negative supply operation, high speed, and high power dissipation.
Legal Metrology • Paper-III
Both the ALU and control section of CPU employ which special purpose storage locations?
A)
Buffers
B)
Decoders
C)
Accumulators
D)
Registers
Correct option: D — Registers. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
If push and pop operation on a stack takes 1 unit time, how much time would it take to delete an element in nth position to bottom?
A)
1
B)
n
C)
n2
D)
Cannot be determined from the given data
Correct option: B — n. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
The purpose of free-wheeling in a thyristor controlled ac to dc converter is to
A)
Reduce the current of its associated thyristor to zero so that commutation can take place
B)
Share the load current of its associated thyristor
C)
Conduct the load current when its associated thyristor is turned off
D)
Maintain voltage across load at constant value
Correct option: C — Conduct the load current when its associated thyristor is turned off. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
In a microprocessor, the register which holds the address of the next instruction to be fetched is
A)
accumulator
B)
program counter
C)
stack pointer
D)
instruction register
Correct option: B — program counter. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
An amplifier with resistive negative feedback has two left half plane poles in its open loop transfer function. The amplifier
A)
will always be unstable at high frequencies
B)
will be stable for all frequencies
C)
may be unstable, depending upon the feedback factor
D)
will oscillate at low frequencies
Correct option: C — may be unstable, depending upon the feedback factor. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
When RET instruction is executed by any subroutine then
A)
the top of the stack will be popped out and assigned to the PC
B)
without any operation, the calling program would resume from instruction immediately following the call instruction
C)
the PC will be incremented after the execution of the instruction
D)
without any operation, the calling program would resume from instruction immediately following the call incremented after the execution of the instruction
RET pops the return address from the stack into the program counter.
Legal Metrology • Paper-III
How many and which types of machine cycles are needed to execute PUSH PSW an Intel 8085 A microprocessor
A)
2, Fetch and memory write
B)
3, Fetch and 2 memory write
C)
3, Fetch and 2 memory read
D)
3, Fetch, Memory read and memory write
TRAP is the highest-priority 8085 interrupt.
Legal Metrology • Paper-III
The synchronisation between micro-processor and memory is done by
A)
ALE signal
B)
HOLD signal
C)
READY signal
D)
None of these
Correct option: C — READY signal. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
In a three phase voltage source inverter operating in a square wave mode, the output line voltage is free from
A)
3rd harmonic
B)
7th harmonic
C)
11th harmonic
D)
13th harmonic
Correct option: A — 3rd harmonic. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
A pre-emphasis circuit provides extra noise immunity by
A)
boosting the bass frequencies
B)
amplifying the higher audio frequencies
C)
pre-amplifying the whole audio band
D)
converting the phase modulation to FM
Pre-emphasis boosts higher audio frequencies before transmission so later de-emphasis improves noise performance.
Legal Metrology • Paper-III
A d.c. chopper has a resistive load of 10 ohms and an input voltage of 220 V. When the chopper switch is ‘ON’, its voltage drop is 2V and the chopping frequency is 1 KHz. If the duty cycle is 50%, then the average output voltage will be
A)
100 V
B)
103 V
C)
106 V
D)
109 V
A low-frequency amplitude modulation is used so the detector output can be measured conveniently.
Legal Metrology • Paper-III
Memory-mapped I/O-scheme for the allocation of address to memories and I/O devices, is used for
A)
small systems
B)
large systems
C)
both large and small systems
D)
very large systems
Reducing lengths to 90% scales 1:1000 to about 1:1111.
Legal Metrology • Paper-III
If two signals modulate the same carrier with different modulation depths of 0.3 and 0.9, the resulting modulation signal will
A)
be over-modulated
B)
have the resultant modulation limited to 1.0
C)
have the resultant modulation index around 0.82
D)
have the resultant modulation index around 0.95
Correct option: A — be over-modulated. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
As compared to full wave rectifier using two diodes, the four diode bridge rectifier has the dominant advantage of
A)
higher current carrying capacity
B)
lower peak inverse voltage requirement
C)
lower ripple factor
D)
higher efficiency
Correct option: B — lower peak inverse voltage requirement. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
In a J-K flip flop the output Q is ‘1’. It does not change when a clock pulse is applied. The possible combination of J and K could be (X denote don’t care)
A)
‘X’ and ‘0’
B)
‘X’ and ‘1’
C)
‘0’ and ‘X’
D)
‘1’ and ‘X’
Correct option: A — ‘X’ and ‘0’. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
The input resistance of a common emitter stage can be increased by: 1. unbypassing emitter resistance, 2. bootstrapping, 3. biasing it at low quiescent current, 4. using compounded BJTs. The correct sequence in descending order of the effectiveness of these methods is
A)
2, 4, 1 and 3
B)
4, 3, 2 and 1
C)
2, 4, 3 and 1
D)
4, 2, 3 and 1
TRAP is the highest-priority 8085 interrupt.
Legal Metrology • Paper-III
In an 8085 microprocessor, the instruction CMP B has been executed while the contents of accumulation is less than of register B. As result carry flag and zero flag will be respectively.
A)
set, reset
B)
reset, set
C)
reset, reset
D)
set, set
TRAP is the highest-priority 8085 interrupt.
Legal Metrology • Paper-III
If a diode is connected anti-parallel with a thyristor, then
A)
both turn-off power loss and turn-off time decrease
B)
turn-off power loss decreases but turn-off time increases
C)
turn-off power loss increases but turn-off time decreases
D)
the arrangement works as a triac
Correct option: D — the arrangement works as a triac. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
In a p+n junction diode under reverse bias, the magnitude of electric field is maximum at
A)
the edge of the depletion region on the p-side
B)
the edge of the depletion region on the n-side
C)
the p+n junction
D)
the centre of the depletion region on the n-side
Correct option: C — the p+n junction. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
In a thyristor dc chopper, which type of commutation results in best performance?
A)
Voltage commutation
B)
Current commutation
C)
Load commutation
D)
Supply commutation
Correct option: A — Voltage commutation. This matches the standard definition/result for the stated question.
Legal Metrology • Paper-III
In a switched-mode power supply (SMPS), after conversion of a.c. supply to a highly filtered d.c. voltage, a switching transistor is switched ON and OFF at a very high speed by a pulse width modulator (PWM) which generates very-high frequency square pulses. The frequency of the pulses typically in the range of
A)
100 Hz-200Hz
B)
500 Hz-1 kHz
C)
2 kHz-5 kHz
D)
20 kHz-50 kHz
A high resistance is connected in series to limit the current through the voltmeter movement.
Legal Metrology • Paper-III
In double sideband suppressed carrier modulation, the modulated wave undergoes phase reversal, whenever
A)
modulating signal’s amplitude decreases
B)
modulating signal’s amplitude increases
C)
modulating signal crosses zero
D)
carrier signal crosses zero
For DSB-SC, a zero crossing of the message changes the carrier multiplier's sign, causing 180° phase reversal.
Legal Metrology • Paper-III
The transmission bandwidth is doubled in FM. The SNR is
A)
also doubled
B)
improved four fold
C)
decreased by one fourth
D)
unaffected
A 7-bit PCM stream at 10 kHz has 70 kb/s bit rate; the corresponding baseband bandwidth is about 35 kHz for ideal Nyquist signaling.
