← MES Jr. Grade
Past Questions
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.
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.
A microprocessor with a 12-bit address bus will be able to access
A)
1 kilobyte of memory
B)
4 kilobytes of memory
C)
8 kilobytes of memory
D)
0.4 kilobytes of memory
A 12-bit address bus can generate 2^12 = 4096 unique addresses. If each address refers to 1 byte of memory, the total accessible memory is 4096 bytes = 4 KB. However, since the options include 4 KB as option (b), that is the correct choice. The other options are incorrect because 1 KB = 1024 bytes, 8 KB would require 13 address bits, and 0.4 KB is far too small.
In a 3-phase semi-converter, the three SCRs are triggered an interval of
A)
60°
B)
90°
C)
120°
D)
180°
In a 3-phase semi-converter, the three SCRs are fired sequentially with a phase displacement of 60° electrical between successive triggering pulses. This is because the three-phase supply has 120° phase separation, and the semi-converter uses one SCR from each phase in a 6-pulse sequence. Hence, the triggering interval between the SCRs is 60°. The other options are incorrect because 90° and 180° do not match the 3-phase firing sequence, and 120° is the phase displacement of the supply phases, not the SCR triggering interval.
For intelligible voice communication, minimum bandwidth required is
A)
900 Hz
B)
1 KHz
C)
3 KHz
D)
6 KHz
For intelligible voice communication, the essential speech frequencies are roughly from 300 Hz to 3400 Hz, so the required bandwidth is about 3 kHz. This is why standard telephone voice channels are designed with a bandwidth of around 3 kHz. 900 Hz and 1 kHz are too narrow for clear speech, while 6 kHz is wider than the minimum required.
Feedback in an amplifier always helps to
A)
control its output
B)
increase its gain
C)
decrease its input impedance
D)
stabilize its gain
Feedback in an amplifier is mainly used to make the amplifier performance less sensitive to variations in transistor parameters, temperature, and supply changes. Negative feedback especially helps stabilize the gain. It does not generally increase gain; in fact, it usually reduces gain but improves stability, bandwidth, and linearity. Hence, the correct answer is 'stabilize its gain'.
The reason of preferring FETs to bipolar transistors in integrated circuits is that
A)
they occupy very small space
B)
it has become a tradition
C)
fabrication of circuit is easy
D)
it is cheaper
FETs are preferred in integrated circuits mainly because they are very small in size and can be packed densely on a chip. This makes IC fabrication more suitable and efficient. Option (b) is irrelevant, (c) is not the main reason compared to density and miniaturization, and (d) is not the primary advantage in this context.
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.
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 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.
An address is the number used by the CPU to specify
A)
a location in the memory
B)
a location in flags
C)
a location in accumulator
D)
a location in stack pointer
An address is a unique number used by the CPU to identify a specific memory location. The CPU uses addresses to read from or write to memory. Flags, accumulator, and stack pointer are CPU registers, not the general meaning of an address.
For small values of drain-to-source voltage, JFET behaves like a
A)
resistor
B)
constant current source
C)
constant voltage source
D)
negative resistance
For a JFET at small drain-to-source voltage (VDS), the channel is not yet pinched off and the drain current increases approximately linearly with VDS. This means it behaves like a voltage-controlled resistor. A constant current source behavior appears in the saturation region at higher VDS, not at small VDS. It is not a constant voltage source, and negative resistance is not the normal operating behavior here.
The modulation index in FM signal depends on
A)
amplitude of the modulating signal
B)
frequency of the modulating signal
C)
both (a) and (b)
D)
none of these
In frequency modulation (FM), the modulation index is defined as β = Δf / fm, where Δf is the frequency deviation and fm is the modulating signal frequency. The frequency deviation Δf is proportional to the amplitude of the modulating signal, so the modulation index depends on the amplitude of the modulating signal as well as the frequency of the modulating signal. Therefore, the correct answer is both (a) and (b).
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.
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.
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.
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.
Which of the following logic Gates are universal Gates?
A)
OR and AND Gates
B)
NOR and NAND Gates
C)
OR and NOR Gates
D)
AND and NAND Gates
Universal gates are those using which any Boolean function can be implemented. NAND and NOR are universal because each can be used alone to realize NOT, AND, and OR operations. OR and AND are not universal by themselves, and the other pairs include at least one non-universal gate.
In a single-phase full converter, if the output voltage has peak and average values of 325 V and 133 V respectively, then the firing angle is
A)
40°
B)
140°
C)
50°
D)
130°
For a single-phase full converter, the average output voltage is given by Vdc = (2Vm/π) cos α, where Vm is the peak value of the supply/output waveform. Here the peak value is 325 V, so the maximum average (at α = 0°) is 2Vm/π ≈ 2×325/π ≈ 206.9 V. Given average output voltage is 133 V, so cos α = 133 / 206.9 ≈ 0.643. Therefore α ≈ cos⁻¹(0.643) ≈ 50°. Hence the correct option is (c) 50°.
A single instruction to clear the lower four bits of the accumulator in 8085 assembly language is
A)
XRIOFH
B)
ANIFOH
C)
XRIFOH
D)
ANOFH
To clear the lower four bits of the accumulator in 8085, we use the logical AND operation with the mask F0H (11110000B). This preserves the upper four bits and resets the lower four bits to 0. In 8085 assembly, the instruction is written as ANI F0H. Among the given options, ANIFOH corresponds to ANI F0H. XOR would not selectively clear only the lower four bits, and the other options are not the correct masking instruction.
In microprocessors, return from a subroutine is affected by
A)
a jump instruction
B)
an RST instruction
C)
a RET instruction
D)
a hardware interrupt signal
In microprocessors, a subroutine is entered using a CALL instruction, and it is returned from using a RET (return) instruction. RET pops the saved return address from the stack and transfers control back to the instruction after the CALL. A jump instruction only transfers control unconditionally, RST is a restart/call-like instruction, and a hardware interrupt signal invokes an interrupt service routine rather than directly returning from a subroutine.
Non-sinusoidal waveforms
A)
are departures from sine waveform
B)
have low mark-to-space ratio
C)
are much easier to generate
D)
are unfit for digital operation
A non-sinusoidal waveform is any waveform that is not a pure sine wave, so it is a departure from sine waveform. Option (b) is not a defining property, (c) is not generally true for all non-sinusoidal waveforms, and (d) is incorrect because many digital signals are non-sinusoidal and are widely used in digital operation.
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 value of Zener current is
A)
limited by external circuit resistance
B)
determined by Zener voltage
C)
totally independent of temperature
D)
always in µA range
In a Zener diode regulator, the Zener current is controlled by the series/external circuit resistance. This resistance limits the current flowing through the diode. It is not fixed solely by the Zener voltage, not totally independent of temperature, and it is not always in the µA range because it can vary from microamps to much higher values depending on the circuit.