← MES Jr. Grade
Past Questions — 2012
A byte is a group of
A)
2 bits
B)
4 bits
C)
8 bits
D)
16 bits
A byte is defined as a group of 8 bits. A bit is the smallest unit of data (0 or 1), and 8 bits together make 1 byte. Therefore, the correct option is (c). Options (a), (b), and (d) are incorrect because 2, 4, and 16 bits correspond to smaller or larger units, not a standard byte.
Modems are used for
A)
modulating digital signals
B)
converting analog to digitals and vice versa
C)
either of these
D)
none of these
A modem (modulator-demodulator) converts digital data into analog signals for transmission and converts received analog signals back into digital form. Hence, its function is conversion between analog and digital signals in both directions. Option (a) is incomplete because modulation is only one part of the modem’s job, and option (c) is incorrect because (a) is not fully accurate as stated.
The input resistance of a MOSFET is
A)
very high as compared to that of a bipolar transistor
B)
low as compared to that of a bipolar transistor
C)
of the same order as of a bi-polar transistor
D)
none of the above
A MOSFET has an insulated gate, so the gate current is almost zero. Therefore its input resistance is extremely high, much higher than that of a bipolar junction transistor (BJT), whose base draws current. Hence option (a) is correct. Options (b) and (c) are incorrect because they describe a much lower input resistance than a MOSFET actually has, and (d) is also incorrect.
A thyristor chopper is preferred over other choppers because it
A)
provides static switching
B)
is economical
C)
can be manufactured easily
D)
none of these
A thyristor chopper is preferred mainly because it is economical compared with other chopper implementations. Thyristors are rugged, reliable, and relatively low-cost devices for high-power switching. Option (a) is not the best reason because all choppers are static electronic switches by nature. Option (c) is not the key advantage, since ease of manufacture is not the primary basis for preference. Therefore, the correct answer is (b) is economical.
The numbers of thyristors required for 1-phase to 1-phase cyloconverter of the mid-point type and for 3-phase to 3-phase 3-pulse type are respectively
A)
4 and 6
B)
4 and 4
C)
4 and 9
D)
4 and 18
For a 1-phase to 1-phase mid-point cycloconverter, two full-wave converters are used, and each needs 2 thyristors, so total = 4 thyristors. For a 3-phase to 3-phase 3-pulse cycloconverter, each 3-pulse converter uses 3 thyristors, and there are 6 such converters in the standard arrangement, so total = 18 thyristors. Hence the correct answer is 4 and 18.
The ASCII code is a
A)
5-bit code
B)
7-bit code
C)
9-bit code
D)
11-bit code
ASCII stands for American Standard Code for Information Interchange. The original ASCII standard uses 7 bits, allowing 128 characters (0 to 127). Therefore, the correct answer is 7-bit code. The other options are incorrect because ASCII is not a 5-bit, 9-bit, or 11-bit code.
A p-n junction photodiode is
A)
operated in forwarded region
B)
encased in an opaque package
C)
a very fast photo detector
D)
dependent on thermally generated minority carriers
A p-n junction photodiode is used as a light detector and is typically operated in reverse bias for fast response. Because of the depletion region and reverse-bias operation, it can respond quickly to changes in light, making it a very fast photo detector. Option (a) is wrong because photodiodes are not normally operated in forward bias. Option (b) is wrong because they must receive light, so they are not placed in an opaque package. Option (d) is wrong because that describes a device whose operation depends mainly on thermally generated minority carriers, not a photodiode.
The main part of an inverter is
A)
oscillator circuit
B)
d.c. source
C)
step up transformer
D)
filter
An inverter converts DC into AC, and its key controlling part is the oscillator circuit, which generates the switching pulses needed to produce alternating output. The DC source only supplies input power, the step-up transformer is used in some inverter designs but is not the main part, and the filter is used to smooth the output waveform.
A D/A converter uses a ladder of +10V full scale output. The number of bits required at its input for a resolution of 5mV is
A)
7
B)
8
C)
9
D)
11
For an n-bit D/A converter, the resolution is approximately Full Scale Output / 2^n. Here, full scale output = 10 V and required resolution = 5 mV = 0.005 V. So, 10 / 2^n <= 0.005, which gives 2^n >= 2000. Since 2^11 = 2048 and 2^10 = 1024, the minimum bits needed is 11 if using exact 10V/2^n. However, in standard DAC MCQ convention, resolution is often taken as Full Scale / (2^n - 1), and for 10V with 5mV step the closest listed answer is 11. But because the options include 8, 9, 11 and the usual exam convention for 10V/256 ≈ 39 mV etc. does not match 8, the mathematically correct choice is 11. Therefore the correct option is (d).
The magnitude of anode current can be controlled in thyristors only by
A)
changing the amplitude of triggered pulse
B)
changing the width of triggered pulse
C)
varying the timing of the triggered pulse with respect to the positive half cycle of the applied voltage
D)
none of these
In a thyristor, the anode current is controlled by controlling the firing angle, i.e., the timing of the gate trigger pulse relative to the positive half-cycle of the applied AC voltage. By delaying or advancing the trigger pulse, the conduction period changes, which changes the average anode current. Changing the amplitude or width of the trigger pulse does not control the anode current in normal thyristor operation.
100% modulation is produced in AM when carrier
A)
frequency equals signal frequency
B)
frequency exceeds signal frequency
C)
amplitude equals signal amplitude
D)
amplitude exceeds signal amplitude
In amplitude modulation (AM), 100% modulation occurs when the modulating signal amplitude is equal to the carrier amplitude, i.e., modulation index m = 1. At this point, the envelope just reaches zero at its minimum without distortion. If the signal amplitude exceeds the carrier amplitude, overmodulation occurs and distortion results. Frequency is not the deciding factor for modulation percentage.
In microprocessor architecture, flag indicates
A)
the number of the microprocessor
B)
the name of the manufacturer
C)
the internal status of the CPU
D)
the bit size of the microprocessor
In a microprocessor, the flag register contains status flags such as zero, carry, sign, overflow, and parity. These flags indicate the internal status of the CPU after arithmetic or logical operations. Therefore, the correct answer is the internal status of the CPU. The other options are incorrect because flags do not represent the processor number, manufacturer name, or bit size.
The effect of noise in a communication system is most adverse with reference to
A)
source
B)
encoder
C)
channel
D)
receiver
Noise is most harmful at the receiver because the receiver must detect and reconstruct the original message from the noisy signal. Any noise added in the channel ultimately degrades the signal quality seen at the receiver, affecting demodulation, decoding, and overall intelligibility. The source and encoder generate/process the message, but the receiver is where the adverse effect of noise is most directly observed.
An amplifier has a power gain of 50. This gain in dB will be
A)
17 dB
B)
31 dB
C)
34 dB
D)
68 dB
Power gain in decibels is given by 10 log10(P2/P1). Here the power gain is 50, so dB gain = 10 log10(50) = 10 × 1.699 ≈ 16.99 dB ≈ 17 dB. Hence, option (a) is correct. The other options do not match the standard decibel conversion for power gain.
The bandwidth of an amplifier may be increased by
A)
decreasing the capacitance of its bypass capacitors
B)
minimizing its stray capacitances
C)
increasing input signal frequency
D)
cascading it
The bandwidth of an amplifier is limited mainly by parasitic and stray capacitances, which create unwanted RC time constants and reduce the high-frequency response. By minimizing these stray capacitances, the upper cutoff frequency increases, so the bandwidth becomes larger. Decreasing bypass capacitor capacitance is not the general method for increasing amplifier bandwidth, increasing input signal frequency does not change the amplifier’s bandwidth, and cascading stages usually reduces overall bandwidth rather than increasing it.
Cycle time of Random Access Memory (RAM) is the time required between successive
A)
access to memory
B)
clocks
C)
delete operations
D)
read/write operations
Cycle time of RAM is the minimum time required between two successive memory operations, i.e., between one read/write operation and the next. It includes the access time plus the recovery time needed by the memory. Hence, the correct choice is read/write operations. The other options are incorrect because clocks are not the definition of RAM cycle time, delete operations are not a standard RAM operation, and access to memory is only part of the cycle time, not the full interval between successive operations.
When a transistor is used as a switch, its operation is confined in
A)
cut-off region
B)
saturation region
C)
active region
D)
both (a) and (b)
When a transistor is used as a switch, it operates only in the two extreme states: cut-off and saturation. In cut-off, the transistor is OFF and no collector current flows. In saturation, the transistor is fully ON and conducts maximum current. The active region is used for amplification, not switching. Therefore, the correct answer is both cut-off and saturation regions.
The main factor which makes a MOSFET likely to break down during normal handling is its
A)
very low gate capacitance
B)
high leakage current
C)
high input resistance
D)
both (a) and (c)
A MOSFET has an insulated gate, so its gate capacitance is very low and its input resistance is extremely high. Because of this, even a small static charge or improper handling can create a large gate-to-source voltage and damage the thin gate oxide. Hence the correct choice is both very low gate capacitance and high input resistance. High leakage current is not the main reason for breakdown during handling.
An SCR is a
A)
two-layer two junction device
B)
three-layer two junction device
C)
four-layer three junction device
D)
four-layer four junction device
An SCR (Silicon Controlled Rectifier) is a PNPN device, meaning it has four layers and three junctions. Hence, it is correctly described as a four-layer three junction device. Option (a) and (b) have too few layers/junctions, and option (d) is incorrect because a four-layer device has only three junctions.
In amplitude modulation
A)
carrier frequency is changed
B)
carrier amplitude is changed
C)
three sidebands are produced
D)
frequency is improved
In amplitude modulation (AM), the amplitude of the carrier wave is varied in accordance with the message signal, while the carrier frequency and phase remain essentially constant. Hence, option (b) is correct. Option (a) describes frequency modulation, option (c) is incorrect because standard AM produces two sidebands, and option (d) is not a property of AM.
The amount of information in a continuous signal is
A)
zero
B)
1
C)
infinite
D)
none of these
A continuous signal can take infinitely many amplitude values over any interval, so it can represent an infinite amount of information in the ideal mathematical sense. Hence the correct choice is (c) infinite. Option (a) is wrong because a continuous signal is not information-free, and (b) is incorrect because the amount is not limited to 1.
In a microprocessor, the address of the next instruction to be executed is stored in
A)
stack pointer
B)
address latch
C)
program counter
D)
general purpose register
The Program Counter (PC) stores the address of the next instruction to be executed in a microprocessor. After each instruction fetch, the PC is automatically updated to point to the following instruction. The stack pointer stores the top of the stack, the address latch temporarily holds address information during bus operations, and general-purpose registers are used for data manipulation, not for tracking the next instruction.
A modulator is a system to
A)
separate two frequencies
B)
impress the information on to a radio frequency carrier
C)
extract information from the carrier
D)
amplify the audio frequency signal
A modulator is used in communication systems to place the message or information signal onto a high-frequency carrier wave for transmission. This process is called modulation. Option (c) describes a demodulator, which extracts information from the carrier. Option (a) is unrelated, and option (d) refers to amplification, not modulation.
Output frequency of inverter circuit depends on
A)
values of the resonant elements
B)
transformation ratio of transformer
C)
level of D.C. voltage applied
D)
none of these
In an inverter circuit, especially a resonant inverter, the output frequency is determined by the resonant frequency of the LC circuit. That resonant frequency depends on the values of the resonant elements, i.e., inductance and capacitance. The transformer ratio does not set the frequency, and the level of DC input voltage mainly affects output magnitude, not frequency.
A mono-stable multivibrator (MMV) is frequently used
A)
in memory and timing circuits
B)
for producing triangular waves
C)
in counting circuits
D)
for generation of distorted waves
A monostable multivibrator has one stable state and one quasi-stable state. When triggered, it produces a single pulse of fixed duration, so it is commonly used in timing circuits and as a memory element for storing a temporary state. It is not used for triangular wave generation, counting circuits, or distorted wave generation.