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21. Pressure of 1 (one) atmosphere is
equivalent to:
(a) 0.101325 MPa
(b) 750 mm of mercury
(c) 1 bar
(d) 0.101325 kPa
OPSC Civil Services
Pre. 2011
Ans. (a) : 1 atmosphere pressure = 101325 Pa = 1.01325 bar = 760 mm of mercury = 760 Torr = 0.101325
MPa=14.6959 Pound-force per square inch.
Answer
22. A steel ball of mass 1 kg and specific
heat 0.4 kJ/kg °C is at a temperature of 60 °C. It is dropped
into 1 kg water at 20 °C. The final steady state temperature of water is :
(a) 23.5 °C
(b) 30 °C
(c) 35 °C
(d) 40 °C
RPSC Vice Principal ITI 2018
Ans. (a)
Answer
23. A 120-V electric resistance heater
draws 10 A. It operates for 10 min in a rigid volume. Calculate the
work done on the air in the volume.
(a) 720000 kJ
(b) 720 kJ
(c) 12000 J
(d) 12 kJ
RPSC Vice Principal ITI 2018
Ans. (b) : W = VIT = 120 V × 10 A × (10 × 60) s = 72 × 104 J = 720 kJ.
Answer
24. Air is compressed in a cylinder such that
the volume changes from 0.2 to 0.02 m3 . The initialpressure is 200 kPa. If the pressure is constant, the
approximate work is
(a) –36 kJ
(b) –40 kJ
(c) –46 kJ
(d) –52 kJ
RPSC Vice Principal ITI 2018
Ans. (a) : Work done, If the pressure is constant,
w = ∫ PdV = P(V2 – V1)
= 200 × (0.02 – 0.2)
= –36 kJ
Answer
25. Match List 1 with List 2 and choose the
correct answer from the
codeList-I (laws of thermodynamics) List-II (Defines)
A.First
(i) Absolute zero temperature
B. Second
(ii) Internal Energy
C. Zeroth
(iii) Temperature
D. Third
(iv) Entropy
1. (A)-(i) (B)-(ii) (C)-(iii) (D)-(iv)
2. (A)-(iii) (B)-(iv) (C-(ii)) (D)-(i)
3. (A)-(iv) (B)-(ii) (C)-(i) (D)-(iii)
4. (A)-(ii) (B)-(iv) (C)-(iii) (D)-(i)
RPSC INSP. OF FACTORIES AND BOILER 2016
Ans : (4)
(A) First→(ii) Internal Energy
(B) Second→(iv) Entropy
(C) Zeroth→ (iii) Temperature
(D) Third → (i) Absolute zero Temperature
Answer
26. Which of the following processes is
irreversible process
(a) Isothermal
(b) Adiabatic
(c) Throttling
(d) All of the above
Vizag Steel (MT) 2017
Ans. (c) : Throttling process in which
No change in enthalpy from state one to state two (h1 = h2)
No work is done (W = 0)
Process called isenthalpic
Process is adiabatic (Q = 0)
Answer
27. A cylinder contains 5m3 of ideal gas at a
pressure of 1 bar. This gas is compressed in a
reversible isothermal process till its pressure increases to 5 bar.
(a) 804.7
(b) 953.2
(c) 981.7
(d) 1012.2
Vizag Steel (MT) 2017
Ans. (a) :
Answer
28. If 'h' refers t heat, T refers to
temperature, then in the throttling process,
(a) h1^2 = h2
(b) h1 = h2
(c) h1 = h2 + (hfg/Ts)
(d) h2 = h1 + (hfg/Ts)
TNPSC 2019
Ans. (b) : The throttling process is a constant enthalpy process. h1 = h2
Answer
29. Which of the following processes are
thermodynamically reversible?
(a) Throttling
(b) Free expansion
(c) Constant volume and constant pressure
(d) Isothermal and adiabatic
TNPSC 2019
Ans. (d) : Throttling, Free expansion, Constant volume and constant pressure processes and adiabatic
process are thermodynamically irreversible whereas isothermal and adiabatic processes are
thermodynamically
reversible.
Answer
30. The most efficient method of compressing
air is to compress it
(a) adiabatically
(b) isentopically
(c) isothermally
(d) isochorically
TNPSC 2019
Ans. (c)
Answer
31. The internal energy of an ideal gas is
function of
(a) pressure only
(b) absolute temperature only
(c) pressure and volume
(d) pressure, volume and temperature
Gujarat PSC AE 2019
TSPSC AEE 2015
UKPSC AE 2007 Paper -II
OPSC AEE 2015 PAPER - II
Ans. (b) : The internal energy of an ideal gas is function of absolute temperature only. U = f (T
only)
Answer
32. Work output from a system is at the expense
of internal energy is a non flow process carried out
(a) at constant pressure
(b) at constant volume
(c) adiabatically
(d) polytropically
TSPSC AEE 2015
Ans. (c) : Work output from a system is at the expense of internal energy is a non flow process carried
out
adiabatically.
Answer
33. The absolute zero pressure will be
(a) When the molecular momentum of the system becomes zero
(b) at sea level
(c) at the temperature of –273K
(d) at the centre of the earth
APPSC AEE 2016
Ans. (a) : Generally, absolute zero pressure is the point where there exist a minimum temperature i.e.
zero. That can be possible only when molecular momentum of system become zero. There should not be any
motion of particles so there is no collision of particles, kinetic energy nullifies and the temperature
becomes zero.
Answer
34. An ideal gas can be taken from point K to
point N in three different paths:
K→L→N, K→N, K→M→N. Which of the following is a true statement?
(a) The same work is done during each process.
(b) The same amount of heat is added to the gas during each process
(c) The same change in internal energy during each process
(d) The same entropy generated during each process
APPSC AEE 2016
Ans. (c) : From this diagram we get that the same change in internal energy during each process because
of
internal energy. It is the property of the system (i.e point function) whereas work and heat for each
process will be different because of area under P–V and T–S diagram will be different for each process
(i.e
path function).
Answer
35. Which of the following is not a property of
the system?
(a) Temperature
(b) Pressure
(c) Volume
(d) Heat
TNPSC AE 2017
UKPSC AE 2012 Paper–II
Ans. (d) : Heat is not a property of the system it is the form of energy whereas temperature, pressure
and
volume are the property of the system.
Answer
36. In reference to Thermodynamic equilibrium,
it is required to have,
(a) Mechanical Equilibrium
(b) Chemical Equilibrium
(c) Thermal Equilibrium
(d) Mechanical, Chemical and Thermal Equilibrium
TNPSC AE 2017 14
Ans. (d) : In reference to Thermodynamic equilibrium, it is required to have, Mechanical, Chemical and
Thermal Equilibrium.
For Mechanical equilibrium ----∆ P≈ 0
For Thermal equilibrium ----∆T ≈ 0
For Chemical equilibrium no change in concentration of reactants and products.
Answer
37. If the value of n is zero in the equation
PV^n = C, then the process is called
(a) constant volume process
(b) constant pressure process
(c) adiabatic process
(d) isothermal process
TNPSC AE 2018
Ans. (b) : If the value of n is zero in the equation pV^n = C, then the process is called constant
pressure
process.
Answer
38. In a free expansion of a gas between two
equilibrium states, work transfer involved.
(a) can be calculated by joining the two states on p-v coordinates by any path and estimating area
below
(b) can be calculated by joining two states by a quasi static path and then finding the area
below
(c) is zero
(d) is equal to heat generated by friction during expansion
TNPSC AE 2018
Ans. (c) : In a free expansion of a gas between two equilibrium states, work transfer involved is
zero.
Answer
39. The internal energy of a substance depends
on
(a) temperature
(b) pressure
(c) entropy
(d) enthalpy
TNPSC AE 2018
Ans. (a) : The internal energy of a substance depends on temperature.
U = mCv∆T
Answer
40. The temperature at which the volume of gas
becomes zero is called
(a) absolute scale of temperature
(b) absolute zero temperature
(c) absolute temperature
(d) dew point temperature
TNPSC AE 2018
Ans. (b) : The temperature at which the volume of gas becomes zero is called absolute zero
temperature.
At absolute zero temperature (– 273.15 K), momentum of gas molecules becomes zero.
Answer
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