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.
41. A fan consumes 20 W of electric power and discharges air from a ventilated room at 0.25 kg/s. The maximum air outlet velocity is nearly
(a) 4.7 m/s (b) 8.7 m/s
(c) 10.2 m/s (d) 12.7 m/s
UPSC JWM 2017
Ans. (d) : Fan convert electrical energy into mechanical energy.
Power = 0.5 Mass flow rate of air × (discharge velocity)^2
Maximum air outlet velocity ≃ 12.7m / s
43. An isolated system-
(a) is a specified region where transfer of energy and/or mass takes place
(b) is a region of constant mass and only energy is allowed to cross the boundaries
(c) cannot transfer either energy or mass to or from the surroundings
(d) is one in which mass within the system is not necessarily constant
RPSC AE 2018
TSPSC AEE 2015
Ans. (c) : Isolated system—An isolated system cannot transfer either energy or mass to or from the surrounding ∆m = 0, ∆E = 0 for isolated system.
Example—Universe, thermal flask bottle etc. 15
44. In the polytropic process equation PV^n = constant if n is infinitely large, the process is termed as-
(a) Constant volume (b) Constant pressure
(c) Constant temperature (d) Adiabatic
RPSC AE 2018
TNPSC AE 2018
UKPSC AE 2007 Paper -II
Ans. (a) : In the polytropic process
PV^n = constant
If n = ∞
then PV ∞ = constant.
Then this polytropic process is termed as costant volume process.
If n = 1
PV = constant (Isothermal process)
If n = 0
PV^0 = constant Constant pressure process
If n = 1.4
PV^1.4 = constant (adiabatic process)
45. The instrument which measures the temperature of the source without direct contact is
(a) Bi-metallic cut-out (b) Vapour pressure thermometer
(c) Pyrometer (d) Thin film thermometer
TNPSC AE 2014
Ans. (c) : Pyrometer–Pyrometer is a device use for measuring relatively high temperature, such as are encountered in furnace. Most pyrometer works by measuring radiation from the body whose temperature is to be measured. Radiation devices have the advantage of not touch the material being measured.
46. Work done for an isothermal process is
(a) (P1V1-P2V2)/n-1 (b) P(V2-V1)
(c)P1V1 ln(P1/P2) (d) P1V1ln(V2/V1)
TNPSC AE 2013
Ans. (c)
47. Which of the following is correct statement for 'Energy (E)'?
(a) 'Energy (E)' is not the property of system
(b) 'Energy (E)' is path function
(c) Change in energy between two states of a system is different for different path followed
(d) For a cyclic process dE= 0
UPRVUNL AE 2016
Ans. (d) : • Energy E is the property of system and it is the point function. • Change in energy between two states of a system is same for different path followed. • For point function dE = 0 for a cyclic process
48. Internal energy of system containing perfect gas depends on
(a) Pressure only (b) Temperature only
(c) Pressure and temperature (d) Pressure temperature and specific heat
HPPSC AE 2018
Ans. (b) : Internal energy of a system containing perfect gas (ideal gas) depends on temperature only.
U = f(T) [For ideal gas only]
49. Which of the following equations is incorrect? (where V,P,T and Q are volume, pressure, temperature and heat transfer respectively)
(a) cyclic integral of dV = 0
(b) cyclic integral of dP = 0
(c) cyclic integral of dT = 0
(d) cyclic integral of dQ = 0
RPSC LECTURER 16.01.2016
Ans. (d):
Because V,P,T are properties of the system whereas Q and work (W) not a properties of the system. Cyclic integration of the system properties will be equal to zero.
50. Which of the following statements is correct for "Energy"
(a) It is a point function (b) It is a path function
(c) It is not a conserved quantity (d) It can be measured by thermometer
RPSC LECTURER 16.01.2016 16
Ans. (a) : Note:-Option (a) is given by RPSC.
51. The heat capacity of the substance is given by expression:
(a) Heat capacity = (Mass) + (specific heat)
(b) Heat capacity = (Mass) – (specific heat)
(c) Heat capacity = (Mass) × (specific heat)
(d) Heat capacity = (Mass) / (specific heat)
(e) Heat capacity = (Mass)^2 + (specific heat)^2
(CGPCS Polytechnic Lecturer 2017)
Ans. (c) : Heat Capacity–Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to a given mass of a material to produce a unit change in its temperature. Heat capacity is an extensive property. It is denoted by C
C = m × c (J/k)
Where m → mass of the system c → Specific heat
52. Which of the following is NOT an intensive thermodynamic property?
(a) Temperature (b) Pressure
(c) Energy (d) Specific volume
(e) Specific energy
(CGPCS Polytechnic Lecturer 2017)
Ans. (c) : Intensive Properties–An intensive property is a property of matter that depends only on the type of matter is a sample and not depends on the amount of mass.
Example–Pressure, temperature, density, viscosity specific enthalpy, specific entropy, specific volume etc.
Extensive Properties– An extensive property is a property that depends on the amount of matter in a sample.
Example– Volume, enthalpy, entropy, mass energy etc.
53. A piston cylinder arrangement has air at 600 kPa, 290 K and volume of 0.01 m^3 . During a constant pressure process, if it gives 54 kJ of work, the final volume must be
(a) 0.10 m^3 (b) 0.05 m^3
(c) 0.01 m^3 (d) 0.15 m^3
JPSC AE PRE 2019
Ans. (a) : Given,
P1 = 600 kPa
T1 = 290 K
W = 54 kJ
V1 = 0.01 m^3
V2 = ?
W = PdV
= P(V2 – V1)
54 × 103 = 600 × 103 (V2 – 0.01)
V2 = 0.1 m^3
54. A polytropic process with n = –1, initiates with P = V = 0 and ends with P = 600 kPa and V = 0.01 m^3 . The work done is
(a) 2 kJ (b) 3 kJ
(c) 4 kJ (d) 6 kJ
JPSC AE PRE 2019
Ans. (b) : Given,
n = –1
P1 = 0
V1 = 0
P2 = 600 kPa
V2 = 0.01 m^3
W = (P1V1-P2V2)/n-1
= 3 kJ
55. Work done in a free expansion process is
(a) Positive (b) Negative
(c) Zero (d) Maximum
JPSC AE PRE 2019
TNPSC AE 2018
UKPSC AE 2007 Paper -II
Ans. (c) : From first law of thermodynamics
δQ = dU + δW,
since, for free expansion (T1 = T2)
δQ = 0 and dU = 0
So, δW = 0
56. For an ideal gas, enthalpy is represented by
(a) H = U – RT (b) H = U + RT
(c) H = RT – U (d) H = –(U + RT)
JPSC AE PRE 2019
Ans. (b) : H = U + PV
PV = mRT
for unity mass, m = 1
H = U + mRT
H = U + RT
57. Which one of the following represents the energy in storage?
(a) Work (b) Heat
(c) Energy (d) Internal energy
JPSC AE PRE 2019
Ans. (d) : Internal energy—Internal energy of a system is the sum of potential energy and kinetic energy of that system.
58. Heat transfer takes place as per
(a) Zeroth Law of Thermodynamics
(b) First Law of Thermodynamics
(c) Second Law of Thermodynamics
(d) Kirchhoff's Law
SJVN ET 2013
Nagaland PSC CTSE 2017 Paper-2
Ans. (c) : Heat transfer takes place as per second law of thermodynamics.
60. 2 kg of substance receives 500 kJ and undergoes a temperature change from 100oC to 200oC. Then average specific heat of substance during the process will be:
(a) 5 kJ/kg K (b) 2.5 kJ/kg K
(c) 10 kJ/kg K (d) 25 kJ/kg K
SJVN ET 2013
Ans. (b) : m = 2kg
Q = 500 kJ
T1 = 100 oC
T2 = 200 oC
Q = mc∆T
500 = 2 × c (200 – 100)
c = 2.5 kJ/kg K
61. Thermocouples are generally used for measuring temperature:
(a) 500°C (b) 1000 °C
(c) 1500°C (d) 2000°C
SJVN ET 2013 TNPSC AE 2018
Ans. (c) : Thermocouples are generally used for measuring temperature up to 1500oC
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