← MES Jr. Grade
Past Questions
The absolute pressure in the condenser of a steam power plant is 2668 Pa and the barometer reading is 760 mm of mercury, then the vacuum recorded in the condenser is
A)
74 cm of mercury
B)
72 cm of mercury
C)
75 cm of mercury
D)
none of these
Vacuum in a condenser = barometric pressure − absolute pressure, expressed in mm/cm of Hg.
Barometer reading = 760 mm Hg = 76 cm Hg.
Absolute pressure in condenser = 2668 Pa.
Since 1 cm Hg ≈ 1333 Pa, 2668 Pa ≈ 2 cm Hg.
Therefore, vacuum = 76 cm Hg − 2 cm Hg = 74 cm Hg.
So the correct option is (a) 74 cm of mercury.
Other options do not match this subtraction result.
Which of the following items is a path function?
A)
Pressure
B)
Temperature
C)
Work
D)
Density
A path function depends on the process or path taken between two states, not just on the initial and final states. Work is a path function because its value changes with the way the process is carried out. Pressure, temperature, and density are state functions, since they depend only on the state of the system.
The fluid forces considered in the derivation of Navier Stokes equation are
A)
gravity, pressure and viscous
B)
gravity, pressure and turbulent
C)
pressure, viscous and turbulent
D)
gravity, viscous and turbulent
The Navier–Stokes equation is derived by applying Newton’s second law to a fluid element and accounting for the main forces acting on it: body force due to gravity, surface force due to pressure, and viscous force due to fluid friction. Turbulent force is not included in the basic derivation of the Navier–Stokes equation.
Thermal diffusivity is
A)
a physical property of the material
B)
function of temperature
C)
a dimensionless parameter
D)
useful in case of radative heat transfer
Thermal diffusivity is a material property defined as α = k / (ρc_p), where k is thermal conductivity, ρ is density, and c_p is specific heat. It indicates how quickly heat spreads through a material. It is not dimensionless, and while it may vary with temperature for some materials, its basic classification is as a physical property of the material. Hence, option (a) is correct.
The internal energy of a perfect gas depends on
A)
temperature and pressure
B)
only temperature
C)
temperature and entropy
D)
temperature and enthalpy
For a perfect gas (ideal gas), internal energy is a function of temperature only. This is because the internal energy depends on molecular kinetic energy, which changes with temperature, and not directly on pressure, entropy, or enthalpy. Hence option (b) is correct. The other options are incorrect because pressure, entropy, and enthalpy are not the sole determining variables for the internal energy of a perfect gas.
Octane number rating is used to determine the ignition quality of fuels for
A)
C.I. engine
B)
S.I. engine
C)
Hydrogen engine
D)
Steam engine
Octane number measures the anti-knock quality of a fuel, i.e., its resistance to premature ignition or knocking. This is used for spark-ignition (S.I.) engines, where the fuel-air mixture is ignited by a spark plug. In contrast, diesel engines (C.I. engines) are rated by cetane number, which indicates ignition quality under compression. Hydrogen and steam engines are not the standard context for octane rating.
For evaporators and condensers, for the given condition, the logarithmic mean temperature difference (LMTD) of parallel flow compared to counter flow is
A)
more
B)
equal
C)
less
D)
may be equal or more
For the same inlet and outlet temperature conditions, the logarithmic mean temperature difference (LMTD) is higher in counter flow than in parallel flow. In evaporators and condensers, this means the parallel-flow arrangement gives a smaller LMTD. Since heat transfer rate is proportional to LMTD, counter flow is generally preferred. Therefore, the LMTD of parallel flow is less than that of counter flow.
A power chopper converts
A)
A.C to D.C.
B)
D.C. to D.C.
C)
D.C. to A.C.
D)
A.C. to A.C.
A power chopper is a static power electronic device used to convert a fixed DC input into a variable DC output. Therefore, it performs DC to DC conversion. The other options correspond to different converters: AC to DC is a rectifier, DC to AC is an inverter, and AC to AC is an AC voltage controller or cycloconverter.
An SCR is also called a
A)
triac
B)
thyristor
C)
diac
D)
unijunction transistor
An SCR (Silicon Controlled Rectifier) is a type of controlled semiconductor device commonly known as a thyristor. It is a four-layer, three-junction device used for switching and rectification. A triac is a bidirectional AC switch, a diac is a two-terminal trigger device, and a unijunction transistor is a different type of transistor used mainly for triggering circuits.
The most useful modulation technique for high fidelity audio broadcasting on radio in current practice is
A)
amplitude modulation
B)
frequency modulation
C)
pulse amplitude modulation
D)
pulse code modulation
High-fidelity audio broadcasting requires better noise immunity and wider bandwidth for improved sound quality. Frequency modulation (FM) is preferred in radio broadcasting because it is much less affected by amplitude noise and provides better audio fidelity than amplitude modulation (AM). Pulse amplitude modulation and pulse code modulation are used in digital/telecommunication systems, not standard radio audio broadcasting.
The FM radio frequency range is approximately
A)
250-300 MHz
B)
150-200 MHz
C)
90-105 MHz
D)
30-70 MHz
FM broadcast radio is commonly allocated around 88 to 108 MHz. Among the given options, 90-105 MHz is the closest and correct approximate range. The other ranges correspond to different frequency bands and are not used for standard FM radio broadcasting.
If the peak value of the input voltage to a half wave rectifier is 28.28 volts and no filter is used the maximum dc voltage across the load will be
A)
20.2V
B)
15 V
C)
9 V
D)
14.14 V
For an ideal half-wave rectifier without filter, the average DC output voltage is Vdc = Vm / π, where Vm is the peak input voltage. Here Vm = 28.28 V, so Vdc = 28.28 / π ≈ 9.0 V. Hence the maximum DC voltage across the load is 9 V. The other options do not match the standard half-wave rectifier average value formula.
When used in circuit, the Zener diode is always
A)
forward-biased
B)
connected in series
C)
troubled by overheating
D)
reverse-biased
A Zener diode is designed to operate in the reverse-bias region, where it maintains an almost constant voltage after breakdown. That is why it is used as a voltage regulator. It is not normally used in forward bias for regulation, and it is not defined by being connected in series or by overheating.
Carrier signal has
A)
constant magnitude
B)
constant frequency
C)
variable frequency
D)
variable time
A carrier signal is a high-frequency sinusoidal wave used to transmit information. In standard communication systems, its frequency remains constant, while its amplitude, phase, or frequency may be varied by the message signal during modulation. Hence, the carrier signal has constant frequency. Option (a) is not generally correct because the carrier’s magnitude may be changed in AM; (c) describes a modulated signal in FM, not the carrier itself; and (d) is not a defining property.
In FM modulation, when the modulation index increases, transmitted power is
A)
Constant
B)
Increased
C)
Decreased
D)
none of these
In frequency modulation (FM), the amplitude of the carrier remains constant; only its frequency varies according to the modulating signal. Since transmitted power depends on carrier amplitude and load resistance, and the amplitude does not change with modulation index, the transmitted power remains constant. Increasing the modulation index only redistributes power among sidebands, but total transmitted power stays the same. Therefore, the correct answer is Constant.
In AM, the carrier is changed by a modulating signal. What parameter of the carrier is changed?
A)
amplitude
B)
frequency
C)
pulse width
D)
phase
In Amplitude Modulation (AM), the amplitude of the carrier wave is varied in accordance with the modulating signal, while its frequency and phase remain essentially constant. Hence, the correct answer is amplitude. Frequency corresponds to FM, phase to PM, and pulse width is related to pulse modulation techniques.
Output of the assembler in machine code is referred to as
A)
Object program
B)
Source program
C)
Macroinstruction
D)
Symbolic instruction
An assembler translates an assembly language source program into machine code. The machine-code output produced by the assembler is called the object program. A source program is the original assembly code, while macroinstruction and symbolic instruction are not the assembler’s machine-code output.
A microprocessor with 12 address line is capable of addressing
A)
1024 locations
B)
2028 locations
C)
4096 locations
D)
64K locations
A microprocessor with 12 address lines can generate 2^12 unique addresses. Since 2^12 = 4096, it can address 4096 memory locations. Option (a) 1024 corresponds to 10 address lines, and (d) 64K corresponds to 16 address lines.
A zener diode
A)
Has a high forward voltage rating
B)
Has a sharp breakdown at low reverse voltage
C)
Is useful as an amplifier
D)
Has a negative resistance
A Zener diode is designed to operate in the reverse-bias breakdown region at a well-defined, low reverse voltage called the Zener voltage. It therefore has a sharp breakdown characteristic. Option (a) is wrong because Zener diodes are not characterized by high forward voltage rating. Option (c) is wrong because they are mainly used for voltage regulation/reference, not amplification. Option (d) is not the best description here; while the breakdown region can show a small dynamic resistance, the defining feature asked in MCQs is the sharp breakdown at low reverse voltage.
A unique advantageous feature of CMOS family is its
A)
use of NMOS circuits
B)
power dissipation in nanowatt range
C)
speed
D)
dependence on frequency for power dissipation
CMOS (Complementary MOS) is known for very low static power consumption compared with TTL and other logic families. Its unique advantageous feature is its extremely low power dissipation, often in the nanowatt range when not switching. Option (a) is incorrect because CMOS uses both NMOS and PMOS transistors, not only NMOS. Option (c) is incorrect because CMOS is generally not chosen for the highest speed. Option (d) is incorrect because power dissipation in CMOS is not the main advantage due to frequency dependence; in fact, dynamic power increases with switching frequency, but the classic distinctive advantage is very low power dissipation.
A common source FET amplifier has a load resistance RL = 500kΩ, rd = 100 kΩ and µ = 24. The voltage gain is
A)
30
B)
25
C)
20
D)
100
For a common source FET amplifier, the voltage gain is approximately A_v = μ(R_D || r_d) / r_d, or equivalently A_v = g_m(R_D || r_d). Here the load resistance is RL = 500 kΩ and the drain resistance is rd = 100 kΩ, so the effective load is the parallel combination: R = (500 × 100)/(500 + 100) kΩ = 83.33 kΩ. Using the given amplification factor μ = 24, the gain becomes A_v = μ × R / rd = 24 × 83.33 / 100 ≈ 20. Thus the correct answer is 20. The other options do not match the calculated gain.
RC coupling is popular in low-level audio amplifiers because it
A)
has better low frequency response
B)
is inexpensive 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 is simple, cheap, compact, and does not require any transformer or special adjustment. It is especially suitable for audio-frequency amplification. Option (a) is incorrect because RC coupling does not give better low-frequency response; transformer coupling is generally poorer at low frequencies, but RC coupling is chosen mainly for economy and simplicity. Option (c) is incorrect because RC coupling does not inherently provide an in-phase output; a common-emitter amplifier gives 180° phase shift. Option (d) is incorrect because the choice of coupling method is not based on needing a low-voltage battery for collector supply.
The POS form of expression is suitable for circuit using
A)
XOR
B)
NAND
C)
AND
D)
NOR
POS means Product of Sums. A POS expression is naturally implemented using OR gates followed by an AND gate, but in universal-gate realizations it is especially suitable for NOR-based circuits because NOR is the dual of OR. Similarly, SOP is more suitable for NAND-based circuits. Therefore, the correct answer is NOR.
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, approximately 530 kHz to 1700 kHz internationally, and commonly taught in exams as 500 kHz to 1500 kHz. Hence option (b) is correct. Option (a) is too low, option (c) is the HF range, and option (d) is the VHF range.
The most highly doped region in a transistor is
A)
base
B)
collector
C)
emitter
D)
both emitter and collector
In a transistor, the emitter is the most heavily doped region because its job is to inject a large number of charge carriers into the base. The base is lightly doped and very thin, while the collector is moderately doped to collect carriers and withstand higher voltage. Therefore, the emitter has the highest doping level.