← MES Jr. Grade
Past Questions — 2012
Out of the following devices, the fastest switching device is
A)
JEFT
B)
BJT
C)
MOSFET
D)
triode
MOSFETs are the fastest switching devices among the given options because they are majority-carrier devices and do not suffer from charge storage delay. A JFET is also a field-effect device, but MOSFETs are generally preferred for very fast switching in digital and power applications. A BJT is slower due to minority-carrier storage effects, and a triode vacuum tube is much slower and obsolete for such applications.
The on-state voltage of a Gate Turn Off (GTO) thyristor is
A)
0.7 V
B)
1.2 V
C)
2.3 V
D)
> 3V
A GTO thyristor has a relatively higher on-state voltage drop than a conventional SCR, typically around 2 to 3 V. Among the given options, 2.3 V is the correct standard value. 0.7 V and 1.2 V are too low and are more typical of low-voltage semiconductor junctions, while > 3 V is generally higher than the usual on-state drop of a GTO.
RC coupling is popular in low-level audio amplifiers because it is
A)
has better low frequency response
B)
is expensive and needs no adjustments
C)
provides an output signal in phase with the input signal
D)
needs low voltage battery for collector supply
RC coupling is widely used in low-level audio amplifiers because it gives good voltage transfer in the audio range and, in a common-emitter amplifier with RC coupling, the output is typically in phase with the input. Option (a) is not the main reason, since RC coupling is not chosen for the best low-frequency response. Option (b) is incorrect because RC coupling is not expensive and does require proper design. Option (d) is unrelated to the advantage of RC coupling.
A converter that can operate in both 3-pulse and 6-pulse mode is
A)
1-phase full converter
B)
3-phase full wave converter
C)
3-phase semi-converter
D)
1-phase semi-converter
A 3-phase full-wave converter can be operated in both 3-pulse and 6-pulse modes depending on the firing arrangement and circuit configuration. In power electronics, the full-wave bridge type allows six-pulse operation in the standard bridge mode, and with suitable connection/operation it can also function as a 3-pulse converter. The other options are incorrect because a 1-phase full converter and 1-phase semi-converter are single-phase circuits, and a 3-phase semi-converter does not provide both 3-pulse and 6-pulse operation in the same way.
Typical bandwidth of an FM receiver is
A)
20 KHz
B)
200 KHz
C)
1 MHz
D)
10 MHz
An FM broadcast signal occupies a much wider bandwidth than AM. By Carson’s rule, the typical FM broadcast bandwidth is about 180 kHz, which is commonly rounded to 200 kHz for an FM receiver. Hence, 200 KHz is the correct choice. 20 KHz is too narrow for FM broadcast, while 1 MHz and 10 MHz are far too large.
The number of diodes required in a bridge rectifier circuit is
A)
one
B)
two
C)
three
D)
four
A bridge rectifier uses four diodes arranged in a bridge configuration. During each half-cycle of AC input, two diodes conduct and two are reverse-biased, but the circuit as a whole requires 4 diodes. Hence, the correct answer is four.
If the drain to source resistance of FET is controlled by the bias voltage VGS, FET is also referred to as a
A)
voltage variable transistor
B)
current variable resistor
C)
voltage variable resistor
D)
current variable transistor
In a FET, the drain-to-source resistance is controlled by the gate-to-source voltage VGS. Since the resistance changes with an applied voltage, the FET is called a voltage variable resistor. Option (a) is incorrect because the device is not usually termed a transistor in this context; option (b) is wrong because the controlling quantity is not current; option (d) is incorrect because the FET is not controlled by current.
The AM broadcast band is given by
A)
10 KHz to 30 KHz
B)
500 KHz to1500 KHz
C)
3 KHz to 30 MHz
D)
30 MHz to 300 MHz
The standard AM broadcast band lies in the medium-frequency range, typically about 530 kHz to 1700 kHz internationally, and in many exam contexts is given approximately as 500 kHz to 1500 kHz. Option (b) matches this band. Option (a) is too low, option (c) is a much wider range covering HF, and option (d) is VHF, not AM broadcast.
An assembler in a computer system prepares
A)
machine-language program from a symbolic language program
B)
object program
C)
assembles computer instructions and data in the machine
D)
none of these
An assembler translates an assembly/symbolic language program into machine language. So option (a) is correct. Option (b) is incomplete because an assembler produces an object program as an intermediate/output form, but the standard definition asked here is the translation from symbolic language to machine language. Option (c) is incorrect because an assembler does not physically assemble instructions and data in the machine.
A program that translates symbolically represented instructions into their binary equivalents is
A)
loader
B)
assembler
C)
linker
D)
autoloader
An assembler translates assembly language, i.e., symbolically represented instructions, into machine code (binary equivalents). A loader loads the executable into memory, a linker combines object files, and an autoloader is not the translation program asked here. Hence, the correct answer is assembler.
In 8085 microprocessor system, the direct addressing instruction is
A)
MOVA, B
B)
MOVB, OAH
C)
MOVC, M
D)
STA addr
In 8085, direct addressing means the instruction contains the 16-bit memory address of the operand explicitly in the instruction.
- STA addr: stores the accumulator directly into the memory location specified by addr, so it uses direct addressing.
- MOV A, B: register addressing, because both operands are registers.
- MOV B, 0AH: this is not a valid 8085 instruction as written; if intended as MVI B, 0AH, that would be immediate addressing.
- MOV C, M: register-indirect addressing, because M refers to the memory location pointed to by HL.
Therefore, the correct answer is STA addr.
The output of each gate is connected to the input of the other and this feedback combination is called
A)
Transistor
B)
MOSFETs
C)
flip-flops
D)
FETs
When the output of each gate is fed back to the input of the other gate, the circuit forms a bistable feedback arrangement. Such a circuit is called a flip-flop. The other options are types of transistors/devices, not feedback memory circuits.
A push-pull amplifier suppresses
A)
only the second harmonic component
B)
only the odd harmonic components
C)
only the even harmonic components
D)
both odd and even harmonic components
In a push-pull amplifier, the two transistors/valves conduct on alternate half-cycles and their outputs are combined in such a way that the even-order harmonics cancel out. This is because the even harmonics are in phase opposition in the two halves, while the odd harmonics add. Therefore, a push-pull amplifier suppresses only the even harmonic components. Option (a) is too specific, and (b) and (d) are incorrect.
For an amplifier, the coupling method which gives the highest gain is
A)
capacitive coupling
B)
resistance coupling
C)
impedance coupling
D)
transformer coupling
Transformer coupling gives the highest gain among the given coupling methods because it can provide impedance matching between stages and transfer maximum power to the load. Capacitive and resistance coupling are common for voltage amplification, but they do not provide as high a gain as transformer coupling. Impedance coupling is also not generally superior to transformer coupling in terms of gain.
Which stage of a D.C. power supply uses a Zener as the main component?
A)
rectifier
B)
voltage divider
C)
regulator
D)
filter
A Zener diode is commonly used in the regulation stage of a D.C. power supply because it maintains an almost constant output voltage despite changes in input voltage or load current. A rectifier converts AC to DC, a filter smooths the pulsations, and a voltage divider only splits voltage—it does not provide regulation.
In AM system, full information can be conveyed by transmitting only
A)
the carrier
B)
the upper sideband
C)
the lower sideband
D)
any one sideband
In amplitude modulation (AM), the information is contained in the sidebands, not in the carrier itself. Since the upper sideband and lower sideband are mirror images and each contains the complete message information, transmitting only one sideband is sufficient to convey full information. The carrier alone carries no information, and a single specified sideband (upper or lower) can be used. Therefore, the correct answer is 'any one sideband'.
The output of a 2-input OR gate is zero only when
A)
both inputs are 0
B)
either input is 0
C)
both inputs are 1
D)
either input is 1
For a 2-input OR gate, the output is 1 if at least one input is 1. Therefore, the output becomes 0 only when both inputs are 0. If either input is 1, the output is 1, so options (b), (c), and (d) are incorrect.
An SCR has
A)
one terminal
B)
two terminals
C)
three terminals
D)
four terminals
An SCR (Silicon Controlled Rectifier) is a thyristor device with three terminals: anode, cathode, and gate. The gate terminal is used to trigger the device into conduction. Hence, the correct answer is three terminals. The other options are incorrect because an SCR is not a one-, two-, or four-terminal device.
Which of the following systems is preferred for chopper drives?
A)
Constant frequency system
B)
Variable frequency system
C)
constant voltage system
D)
none of these
Chopper drives are generally preferred with a constant frequency system because it gives better control, simpler design, and easier filtering of ripple. In chopper control, the output voltage is varied by changing the duty ratio while keeping the switching frequency fixed. Variable frequency systems are more common in some other drive/control schemes, but for chopper drives constant frequency operation is preferred. Hence, option (a) is correct.
The most commonly used filters in SSB generation are
A)
RC
B)
mechanical
C)
LC
D)
low pass
In SSB generation, the filter method commonly uses band-pass or crystal/LC filters to select one sideband and suppress the other. Among the given options, LC is the most commonly used practical filter type. RC filters are generally used at lower frequencies and mechanical filters are not the usual standard answer here. ‘Low pass’ is not the typical answer for SSB generation filters.
The frequency of an Astable Multivibrator (AMV) depends mainly on
A)
value of collector load resistors
B)
RC values of the circuit
C)
value of transistor β
D)
width of the input pulse
In an astable multivibrator, the oscillation frequency is determined mainly by the charging and discharging time constants of the timing network, i.e., the RC values. The resistors and capacitors set the period of each half-cycle. Collector load resistors affect circuit operation but are not the main factor for frequency. Transistor β has little effect on the oscillation frequency, and width of input pulse is irrelevant because an astable multivibrator has no stable state and does not require an input pulse.
A PIN photodiode has ultrafast response due to
A)
the presence of middle I-layer
B)
heavy doping of P and N regions
C)
higher electrical conductivity of Si
D)
the wide spectral response
A PIN photodiode has an intrinsic (I) layer between the P and N regions. This wide depletion region reduces junction capacitance and allows faster carrier collection, giving an ultrafast response. Heavy doping would increase recombination, higher conductivity of Si is not the reason for speed, and wide spectral response is unrelated to response time.
The number of flip flops required in a decade counter is
A)
2
B)
3
C)
4
D)
10
A decade counter counts 10 states (0 to 9). The number of flip-flops required is the smallest n such that 2^n >= 10. Since 2^3 = 8 is not enough and 2^4 = 16 is sufficient, 4 flip-flops are required. Hence, option (c) is correct.
The potential barrier existing across a PN junction
A)
facilitates recombination of electrons and holes
B)
prevents flow of minority carriers
C)
prevents total recombination of holes and minority carriers
D)
prevents neutralization of acceptor and donor ions
In a PN junction, diffusion of electrons and holes near the junction leaves behind fixed ionized donor ions on the N-side and ionized acceptor ions on the P-side. This creates the depletion region and the built-in potential barrier. The barrier opposes further diffusion and thus prevents the neutralization of these immobile donor and acceptor ions. Option (a) is wrong because the barrier actually opposes carrier movement rather than facilitating recombination. Option (b) is incorrect because minority carriers are mainly affected by the junction field in reverse bias, not by the definition of the barrier itself. Option (c) is vague and not the correct physical description.
In FM, when frequency deviation is doubled
A)
modulation is doubled
B)
modulation is halved
C)
carrier swing is halved
D)
modulation index is decreased
In frequency modulation (FM), the modulation index is directly proportional to the frequency deviation. If the frequency deviation is doubled, the modulation index also doubles. Therefore, the correct option is (a) modulation is doubled. The other options are incorrect because halving the modulation or carrier swing would happen if deviation decreased, and the modulation index does not decrease when deviation increases.