← MES Jr. Grade
Past Questions
Total emissivity of a polished silver surface compared to black body is
A)
same
B)
more or less same
C)
higher
D)
lower
A black body has the maximum possible emissivity, equal to 1. A polished silver surface is highly reflective and emits very little thermal radiation, so its total emissivity is much lower than that of a black body. Hence the correct answer is 'lower'.
Gas turbine usually operates on
A)
constant volume cycle
B)
constant pressure cycle
C)
dual combustion cycle
D)
constant temperature cycle
A gas turbine works on the Brayton cycle, in which heat addition and heat rejection ideally occur at constant pressure. Hence, the usual operating cycle is the constant pressure cycle. The other options refer to different ideal cycles: constant volume is Otto cycle, dual combustion is used in diesel engine analysis, and constant temperature is not the standard gas turbine cycle.
By taking the ratio of pressure force and inertia force, the following number may be obtained
A)
Weber number
B)
Euler number
C)
Froude number
D)
Mach number
The Euler number is defined as the ratio of pressure force to inertia force in fluid flow. It is commonly written as Eu = p / (ρV^2) in nondimensional form.
Why others are incorrect:
- Weber number = inertia force / surface tension force.
- Froude number = inertia force / gravitational force.
- Mach number = flow velocity / speed of sound.
Therefore, the correct answer is Euler number.
The refrigerant used in vapour absorption refrigerator is
A)
freon-12
B)
ammonia
C)
aqua-ammonia
D)
carbon di-oxide
In a vapour absorption refrigerator, the working pair is commonly ammonia as the refrigerant and water as the absorbent, together called aqua-ammonia. Hence, aqua-ammonia is the correct answer. Freon-12 is mainly used in vapour compression systems, and carbon dioxide is not the standard refrigerant for vapour absorption refrigerators in such exam context.
Surge tank is provided to protect the
A)
generator
B)
hydraulic turbine
C)
scroll case
D)
penstock
A surge tank is installed in a hydropower system to absorb sudden pressure changes caused by rapid load variations. It protects the penstock from water hammer and excessive pressure rise or drop. Hence, the correct answer is penstock. The generator, turbine, and scroll case are not the primary components protected by a surge tank.
Total heat of a substance is also known as
A)
internal energy
B)
entropy
C)
latent heat
D)
enthalpy
Total heat of a substance is called enthalpy. Enthalpy is defined as H = U + pV, where U is internal energy. It represents the total heat content of a system at constant pressure. Internal energy is only the energy contained within the system, entropy is a measure of disorder, and latent heat is the heat absorbed or released during a change of state.
A floating body is said to be in a state of stable equilibrium
A)
when its metacentric height is zero
B)
when the metacentre is above the centre of gravity
C)
when the metacentre is below the centre of gravity
D)
only when the centre of gravity is below its centre of buoyancy
For a floating body, stability depends on the relative positions of the metacentre (M) and centre of gravity (G). If M is above G, the metacentric height is positive, so after a small tilt the restoring couple brings the body back to its original position. Hence the body is in stable equilibrium. If M and G coincide, equilibrium is neutral. If M is below G, the body is unstable. Therefore, option (b) is correct.
The ideal efficiency of a simple gas turbine depends upon
A)
temperature ratio
B)
pressure ratio
C)
volume ratio
D)
mass ratio
For an ideal simple gas turbine (Brayton cycle), thermal efficiency depends primarily on the pressure ratio. In the ideal cycle, higher pressure ratio generally improves efficiency up to a limit. Temperature ratio is not the direct controlling parameter in the standard expression for simple gas turbine efficiency. Volume ratio and mass ratio are not the governing factors for ideal cycle efficiency.
The ratio of Cp to Cv of a perfect gas is called
A)
isothermal index
B)
adiabatic index
C)
ideal gas index
D)
isentropic index
For a perfect gas, the ratio Cp/Cv is denoted by γ (gamma). This ratio is called the adiabatic index, because it appears in adiabatic relations for gases. The other options are not the standard term used for Cp/Cv.
Practically all the engineering processes are
A)
quasi-static
B)
reversible
C)
irreversible
D)
thermodynamically equilibrium
In real engineering practice, processes occur with friction, heat loss, unrestrained expansion, finite temperature differences, and other dissipative effects. Because of these irreversibilities, practically all engineering processes are irreversible.
Why others are incorrect:
- (a) Quasi-static processes are idealized and occur infinitely slowly; real processes are not practically quasi-static.
- (b) Reversible processes are ideal limits and cannot be achieved in practice.
- (d) Thermodynamic equilibrium describes a state, not the general nature of real engineering processes.
Willan’s line is a straight line graph between the rate of steam consumption and
A)
pressure of steam
B)
temperature of steam
C)
indicated horse power
D)
none of these
Willan’s line is the straight-line relationship between steam consumption and indicated power (indicated horse power, IHP) of an engine at constant speed and cut-off. As load increases, steam consumption varies approximately linearly with IHP. It is not a graph with pressure or temperature of steam, so options (a) and (b) are incorrect. Hence, the correct answer is indicated horse power.
Bernoulli’s theorem deals with the law of conservation of
A)
mass
B)
energy
C)
momentum
D)
none of these
Bernoulli’s theorem states that for an ideal fluid flowing steadily, the sum of pressure energy, kinetic energy, and potential energy remains constant along a streamline. Therefore, it is based on the law of conservation of energy. Mass is conserved by the continuity equation, and momentum is related to Newton’s second law, not Bernoulli’s theorem.
Which of the following rotary types is a positive displacement compressor?
A)
radial flow turbo compressor
B)
axial flow turbo compressor
C)
screw type compressor
D)
mixed flow compressor
A positive displacement compressor traps a fixed volume of air and then reduces its volume to increase pressure. A screw type compressor is a rotary positive displacement compressor because air is compressed between rotating helical screws. In contrast, radial flow turbo, axial flow turbo, and mixed flow compressors are dynamic compressors, not positive displacement types.
The refrigeration effect from a flooded evaporator as compared to a dry evaporator fitted in a similar plant is
A)
more
B)
less
C)
equal
D)
unpredictable
A flooded evaporator generally gives a higher refrigeration effect than a dry evaporator in a similar plant. In a flooded system, the evaporator surface remains fully wetted with liquid refrigerant, so heat transfer is better and the refrigerant can absorb more heat before leaving the evaporator. In a dry evaporator, part of the surface may not be effectively utilized, so the refrigeration effect is comparatively lower. Hence, the correct answer is 'more'.
In the FM wave described by equation v = 15 sin (4 × 10^8 t + 3 sin 1100 t), the maximum frequency deviation is
A)
175 Hz
B)
525 Hz
C)
58.33 Hz
D)
3 Hz
For an FM wave of the form v = A sin(ωc t + β sin ωm t), the coefficient of sin ωm t is the modulation index β. Here, β = 3 and ωm = 1100 rad/s. The maximum frequency deviation is Δf = β fm, where fm = ωm / (2π) = 1100 / (2π) ≈ 175 Hz. So Δf = 3 × 175 = 525 Hz. Hence, the correct answer is 525 Hz.
The rate at which information can be carried through a communication channel depends on
A)
carrier frequency
B)
bandwidth
C)
transmission loss
D)
transmitted power
The information-carrying capacity of a communication channel is primarily determined by its bandwidth. According to Shannon’s channel capacity concept, a wider bandwidth allows more information to be transmitted per unit time. Carrier frequency does not directly decide capacity, while transmission loss and transmitted power affect signal quality and range, not the basic channel capacity in the same direct way as bandwidth.
The bandwidth of DSB suppressed carrier modulation system when the modulating frequency varies between 500 Hz and 5 kHz is
A)
555 kHz
B)
505 kHz
C)
500 kHz
D)
9 kHz
In DSB-SC (Double Sideband Suppressed Carrier) modulation, the bandwidth is twice the highest modulating frequency: BW = 2f_m(max). Here the modulating frequency varies up to 5 kHz, so BW = 2 × 5 kHz = 10 kHz. However, among the given options, the closest and intended exam answer is 9 kHz, which likely reflects a question/printing error. If the question is interpreted strictly, the correct theoretical bandwidth should be 10 kHz, but since 10 kHz is not listed, option (d) is the only plausible choice provided.
If a line is terminated in characteristic impedance Z0; the input impedance measured at the input will be
A)
Z0
B)
Z0 /2
C)
zero
D)
infinite
For a transmission line terminated in its characteristic impedance Z0, there is no reflection at the load. Hence the input impedance seen at the sending end equals the characteristic impedance itself, i.e., Z_in = Z0. Therefore, the correct option is (a). The other options are incorrect because Z0/2, zero, and infinite input impedance occur only under special mismatched or open/short-circuited conditions, not when the line is properly matched.
The characteristic impedance of a cable is about
A)
2 Ω
B)
5 Ω
C)
50 Ω
D)
300 Ω
The characteristic impedance of a cable is typically around 50 Ω for standard transmission/coaxial cables. This is a widely used nominal value in electrical and communication engineering. 2 Ω and 5 Ω are far too low, while 300 Ω is more typical of certain twin-lead transmission lines, not the usual cable characteristic impedance asked here.
The velocity of sound waves in air
A)
is constant at all temperatures
B)
varies directly as temperature
C)
varies inversely as absolute temperature
D)
varies directly as square root of absolute temperature
The speed of sound in air is given by v = \u221a(\u03b3RT/M), so it is proportional to the square root of the absolute temperature (in Kelvin). Hence, as temperature increases, sound velocity increases as \u221aT. Option (a) is wrong because velocity changes with temperature, (b) is wrong because it is not directly proportional to T, and (c) is wrong because it does not vary inversely with temperature.
Narrowband FM signal can be considered to be equal to
A)
PM
B)
AM
C)
SSB
D)
DSB
For narrowband FM, the modulation index is very small, so the FM signal can be approximated by a carrier plus two sidebands. This makes it equivalent to a double sideband (DSB) signal with a carrier component. It is not exactly AM, PM, or SSB. Hence, the correct answer is DSB.
For AM receivers the standard IF frequency is
A)
106 KHz
B)
455 KHz
C)
1.07 MHz
D)
10.7 MHz
In standard AM broadcast receivers, the intermediate frequency (IF) is conventionally 455 kHz. This value is widely used because it provides a good compromise between selectivity, image-frequency rejection, and ease of filter design. Option (d) 10.7 MHz is the standard IF for FM receivers, not AM. Option (c) 1.07 MHz is too high for standard AM IF, and (a) 106 kHz is not the usual standard.
In single tone AM modulation, the transmission efficiency for m=1 is
A)
33.3%
B)
50%
C)
100%
D)
16.65%
For single-tone AM, transmission efficiency is the ratio of sideband power to total transmitted power: η = m^2 / (2 + m^2). For m = 1, η = 1 / (2 + 1) = 1/3 = 33.3%. Hence the correct option is (a). Option (b) 50% is not correct for standard AM, (c) 100% is impossible in conventional AM, and (d) 16.65% is too low.
A rectangular waveguide has width a. Then the cutoff frequency (with corresponding wavelength λ) is
A)
a= λ/2
B)
a= λ/C
C)
a= λ/4
D)
a=2λ
For a rectangular waveguide, the cutoff condition for the dominant mode (TE10) occurs when the guide width equals half the cutoff wavelength. Hence, a = λ/2. The other options do not match the standard cutoff relation for rectangular waveguides.
Describe the flag registers in 8085 microprocessor.