← MES Jr. Grade
Past Questions
Which of the following is an extensive property of a thermodynamic system?
A)
Pressure
B)
Volume
C)
Temperature
D)
Density
An extensive property depends on the size or mass of the system. Volume increases when the amount of substance increases, so it is extensive. Pressure, temperature, and density do not depend on system size, so they are intensive properties.
The compression ratio of Petrol engine is in the range of
A)
2 to 3
B)
7 to 10
C)
16 to 20
D)
above 20
In a petrol (spark-ignition) engine, the compression ratio is generally kept moderate to avoid knocking. Typical compression ratios are in the range of about 7:1 to 10:1. Option (a) is too low for normal petrol engines, while (c) and (d) are characteristic of diesel engines, which use much higher compression ratios.
If a refrigerant is having low specific heat, then coefficient of performance (COP) will be
A)
lower
B)
higher
C)
same
D)
none of these
A refrigerant with low specific heat absorbs less sensible heat in the liquid state before evaporation, so the refrigeration effect per unit mass increases relative to the compressor work in many standard cycle comparisons. Hence the coefficient of performance (COP) tends to be higher. Therefore, the correct option is (b) higher.
A refrigerator works on
A)
Bell-Coleman cycle
B)
reversed Carnot cycle
C)
Carnot cycle
D)
both (a) and (b)
A refrigerator is a heat pump operating on a reversed cycle. In theory, the ideal refrigerator works on the reversed Carnot cycle, which gives the maximum possible COP. In practical air refrigeration systems, the Bell-Coleman cycle is used. Since both are associated with refrigerator operation, the correct option is both (a) and (b).
Temperature of air recorded by an ordinary thermometer is known as
A)
wet bulb temperature
B)
dry bulb temperature
C)
dew point temperature
D)
saturation temperature
The temperature of air measured by an ordinary thermometer exposed to the air is called the dry bulb temperature. A wet bulb thermometer gives wet bulb temperature, dew point is the temperature at which moisture starts condensing, and saturation temperature refers to the temperature at which air becomes saturated with water vapour.
All gases tend to ideal or perfect gas behavior at all temperatures as their pressure approaches
A)
Atmospheric
B)
Zero
C)
Maximum
D)
Critical
Real gases approach ideal or perfect gas behavior when their pressure becomes very low, i.e., as pressure approaches zero. At low pressure, intermolecular forces and molecular volume effects become negligible, so the gas follows the ideal gas law more closely. Atmospheric, maximum, and critical pressures do not generally make gases behave ideally.
The pressure on the two sides of the impulse wheel of a steam turbine
A)
is same
B)
is different
C)
increases from one side to other side
D)
decreases from one side to other side
In an impulse turbine, the entire pressure drop occurs in the nozzles before the steam strikes the moving blades. The impulse wheel/blades work at nearly constant pressure on both sides, so there is no pressure difference across the wheel. Hence, the pressure on the two sides of the impulse wheel is the same. Options (b), (c), and (d) are incorrect because pressure variation across the moving blades is a feature of reaction turbines, not impulse turbines.
In an extensive property of a thermodynamic system
A)
Extensive heat is transferred
B)
Extensive work is done
C)
Extensive energy is utilized
D)
None of the above
An extensive property depends on the size or mass of the system, such as mass, volume, total energy, and entropy. Heat and work are not properties; they are path functions, so the terms 'extensive heat' and 'extensive work' are incorrect. 'Extensive energy' is also not the standard statement here because energy is a property, but the question asks what is done/transferred in an extensive property context, and none of the given statements is correct.
In a refrigeration cycle, the moisture is to be removed before it enters the
A)
cold side of system
B)
evaporator
C)
compressor
D)
condenser
In a refrigeration cycle, moisture must be removed from the refrigerant before it enters the compressor. If moisture enters the compressor, it can cause corrosion, oil dilution, and possible mechanical damage. Therefore, a drier is used to remove moisture before the compressor. The evaporator and condenser are not the components where moisture removal is required in this context.
For a closed system, the difference between the heat added to the system and the work done by the gas, is equal to the change in
A)
enthalpy
B)
entropy
C)
internal energy
D)
temperature
For a closed system, the first law of thermodynamics gives: Q - W = ΔU, where Q is heat added to the system, W is work done by the gas, and ΔU is the change in internal energy. Therefore, the difference between heat added and work done equals the change in internal energy. Enthalpy, entropy, and temperature are not given by this direct relation.
The thermal efficiency of the engine with condenser compared to one without condenser, for a given pressure and temperature of steam is
A)
higher
B)
lower
C)
unaffected
D)
same so long temperature remains constant
A steam engine with a condenser operates at a lower exhaust pressure (vacuum at the outlet). This increases the pressure drop across the engine, so the steam does more work during expansion. For the same steam pressure and temperature at admission, the cycle efficiency therefore increases. Hence, compared to an engine without a condenser, the thermal efficiency is higher.
Brine is always used as a secondary refrigerant in a
A)
cold storage plants
B)
milk chilling plants
C)
cinema hall air conditioning plants
D)
ice plants
Brine is a common secondary refrigerant used in cold storage plants because it can circulate through coils and maintain low temperatures without freezing easily. In such systems, the primary refrigerant cools the brine, and the brine then carries the cooling effect to the storage space. Milk chilling plants and cinema hall air conditioning plants generally use direct refrigeration or chilled water systems, while ice plants use direct refrigeration for ice making rather than brine as the usual secondary refrigerant.
The reheat factor in steam turbine depends on
A)
exit pressure only
B)
stage efficiency only
C)
initial pressure and temperature only
D)
all the above
The reheat factor in a steam turbine is influenced by the turbine operating conditions and stage performance. It depends on the exit pressure, stage efficiency, and also the initial steam pressure and temperature. Hence, all the given factors affect the reheat factor. Therefore, option (d) is correct.
A fluid in which resistance of deformation is independent of the shear stress is known as
A)
Bingham plastic fluid
B)
Pseudo plastic fluid
C)
Dilatent fluid
D)
Newtonian fluid
A Newtonian fluid is one in which the viscosity (resistance to deformation) is constant and independent of the applied shear stress. In such fluids, shear stress is directly proportional to rate of shear strain. Bingham plastic fluids require a yield stress before they start flowing, while pseudo plastic and dilatent fluids are non-Newtonian and their viscosity changes with shear rate.
The refrigerant used in vapour absorption refrigerator is
A)
Freon-12
B)
Ammonia
C)
CO2
D)
Aqua-ammonia
In a vapour absorption refrigeration system, the common working pair is ammonia as the refrigerant and water as the absorbent, called aqua-ammonia. Hence the refrigerant used is aqua-ammonia. Freon-12 is mainly used in vapour compression systems, while CO2 is not the standard answer here.
The coefficient of performance (COP) of a refrigerator working on a reversed Carnot cycle is 5. The ratio of highest absolute temperature to lowest temperature would be
A)
1.25
B)
1.3
C)
1.4
D)
1.2
For a refrigerator working on a reversed Carnot cycle,
COP = T_L / (T_H - T_L).
Given COP = 5,
5 = T_L / (T_H - T_L).
So, 5(T_H - T_L) = T_L
=> 5T_H - 5T_L = T_L
=> 5T_H = 6T_L
=> T_H / T_L = 6/5 = 1.2.
Hence, the ratio of highest absolute temperature to lowest absolute temperature is 1.2. The other options do not satisfy the Carnot COP relation.
In reciprocating air compressor the method of controlling the quantity delivered is done by
A)
throttle control
B)
blow-off control
C)
clearance control
D)
all of the above
In a reciprocating air compressor, the quantity delivered can be controlled by several methods: throttle control, blow-off control, and clearance control. Throttle control reduces the intake pressure, blow-off control diverts excess air, and clearance control varies the clearance volume to reduce delivery. Since all three are valid methods, the correct answer is 'all of the above'.
In a four stroke cycle engine, the four operations namely suction, compression, expansion and exhaust are completed in the number of revolutions of crank shaft equal to
A)
four
B)
three
C)
two
D)
one
In a four-stroke engine, one complete cycle requires 4 strokes of the piston: suction, compression, expansion (power), and exhaust. Since the crankshaft completes 2 revolutions for these 4 strokes, the correct answer is two revolutions. Hence, option (c) is correct.
The Zeroth law deals with thermal equilibrium and establishes a concept of following
A)
Thermal energy
B)
Temperature
C)
Heat
D)
Temperature
The Zeroth law of thermodynamics states that if two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other. This law establishes the concept of temperature as the property that determines thermal equilibrium. Hence, it deals with and defines the concept of temperature. Thermal energy and heat are different concepts, and option (d) is a duplicate of (b).
The bank of tubes at the back of domestic refrigerator are
A)
condenser tubes
B)
evaporated tubes
C)
refrigerant cooling tubes
D)
capillary tubes
In a domestic refrigerator, the coil/tube arrangement at the back is the condenser. It rejects heat from the hot, high-pressure refrigerant to the surrounding air, so the refrigerant condenses there. The evaporator is inside the cabinet, capillary tubes are small metering tubes, and 'refrigerant cooling tubes' is not the standard term.
A thermocouple consists of two dissimilar metals or alloys which develop e.m.f. when the reference and measuring junctions are at different level of
A)
Voltage
B)
Temperature
C)
Flux
D)
Thermions
A thermocouple works on the Seebeck effect: when the measuring junction and reference junction are at different temperatures, an e.m.f. is produced. Hence the correct answer is Temperature. Voltage, flux, and thermions are not the operating principle of a thermocouple.
Coefficient of performance of a domestic refrigerator as compared to that of an air conditioner is generally
A)
more
B)
less
C)
same
D)
none of these
The coefficient of performance (COP) of a domestic refrigerator is generally higher than that of an air conditioner. A refrigerator usually operates with a smaller temperature lift between the evaporator and condenser, so it requires less work per unit of refrigeration effect. Hence its COP is more. An air conditioner typically has a larger cooling load and often a larger temperature difference, so its COP is comparatively lower.
The ratio of specific heats of a gas at constant pressure and at constant volume
A)
varies with temperature
B)
varies with pressure
C)
is always constant
D)
none of the above
The ratio of specific heats is denoted by γ = Cp/Cv. For a given gas in the ideal-gas approximation, Cp and Cv are constants for a fixed composition, so their ratio is also constant. Hence the correct option is (c). Options (a) and (b) are not generally true for the standard thermodynamics treatment used in such exams.
Which one of the following components is not boiler mounting?
A)
Safety valve
B)
Pressure gauge
C)
Feed pump
D)
Stop valve
Boiler mountings are the essential fittings attached to a boiler for safe operation. Safety valve, pressure gauge, and stop valve are all boiler mountings. A feed pump is not a mounting; it is a boiler accessory used to supply water to the boiler.
The refrigerant used in air craft is
A)
Ammonia
B)
CO2
C)
air
D)
Freon -12
In aircraft refrigeration systems, air is commonly used as the refrigerant because it is safe, light, readily available, and suitable for air-cycle refrigeration. Ammonia is toxic, CO2 is not the standard choice for aircraft cooling, and Freon-12 is used in vapour compression systems but not typically for aircraft refrigeration in this context.