# Thermodynamics Test Questions - Set - 8

1)   The substance which is homogeneous and invariable in chemical composition throughout its mass is called as ____.

a. ideal substance
b. pure substance
c. solid substance
d. none of the above
 Answer  Explanation  Related Ques ANSWER: pure substance Explanation: Pure substances have homogeneous and invariable chemical composition throughout its mass. Atmospheric air, combustion products of fuel are the examples of pure substance.

2)   The two-property rule statement consists that ____.

a. to fix state of pure substance of a given mass, the system should be in equilibrium
b. to fix state of pure substance of a given mass, any two independent intensive properties of the substance should be specified
c. both a. and b. conditions should be satisfied
d. none of the above
 Answer  Explanation  Related Ques ANSWER: both a. and b. conditions should be satisfied Explanation: The state of pure substance of a given mass can be fixed by specifying two independent intensive properties when the system is in equilibrium. Once any two properties of a pure substance is known then other properties can be calculated from available thermodynamic relations.

3)   Absolute pressure is measured as

a. Gauge pressure – Atmospheric pressure
b. Gauge pressure + Atmospheric pressure
c. Gauge pressure / Atmospheric pressure
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Gauge pressure + Atmospheric pressure Explanation: Most pressure measuring instruments indicate pressure relative to the atmospheric pressure, Whereas the pressure of a system is its pressure above zero, or relative to a perfect vacuum. The pressure relative to the atmosphere is called as gauge pressure. The pressure relative to the perfect vacuum is called as absolute pressure.

4)   A platinum resistance thermometer has a resistance of 2 ohm at 0° C and 3 ohm at 100° C. What will be the temperature when resistance indicates 5 ohm?

a. 300° C
b. 200° C
c. 350° C
d. 400° C
 Answer  Explanation  Related Ques ANSWER: 300° C Explanation: The resistance and temperature relation is given by R = R0 (1 + αt) by electric resistance thermometer.where R0 is the resistance at 0° CR0 = 2 ohmR100 =3 ohm = (1 + α 100)Therefore α = 0.005Now, R= 5 ohm5 = 2 (1 + 0.005t)t = 300° C

5)   Heat flow is a quantity of heat transfer

a. within definite time
b. within definite cross-sectional area
c. within definite volume of the system
d. none of the above
 Answer  Explanation  Related Ques ANSWER: within definite time Explanation: The direction of the heat transfer takes place from a body with higher temperature to a body with lower temperature. The heat transfer takes place through all directions of the system with different rates of heat transfer. Heat transfer with a certain rate is a heat flow. Heat flow can be defined as a quantity of heat transfer within definite time. Q is the symbol of heat flow. If heat flows into a system then it is considered positive and if heat flows out of the system then it is considered as negative.

6)   The process in which no heat transfer takes place through boundaries is called as

a. isothermal process
c. isochoric process
d. none of the above
 Answer  Explanation  Related Ques ANSWER: adiabatic process Explanation: In adiabatic process, no heat crosses the boundaries of the system. Therefore no heat transfer takes place in adiabatic process. There is only work interaction between system and surrounding in adiabatic process. And the wall or boundary which does not allow the heat to flow through it is called as adiabatic wall and the wall which allows the heat to flow through it is called as diathermic wall. Isothermal process is the process in which temperature is constant. In isothermal process, the heat flows into or out of the system is very slow to maintain thermal equilibrium. Isochoric is the constant volume process.

7)   Heat transfer is

a. a point function
b. a path function
c. a transfer function
d. none of the above
 Answer  Explanation  Related Ques ANSWER: a path function Explanation: The quantity of heat transfer that is heat flow Q can be determined in terms of the work W in the same process. Work involved in a process is not the same because it depends upon the path through which the process is carried out. The work involved in a process is not conserved. But, the difference (Q – W) is conserved for all the paths between the two states in a process, because of principle of conservation of energy. Therefore, heat flow Q, like W, depends on the path through which the process is carried out. Heat flow is path-dependent not a property. Therefore heat transfer is a path function. The amount of heat transfer when a system changes from state 1 to state 2 depends on the paths through which the system passes.

8)   The equation for calculating amount of heat transfer through a system boundary
when,
T is temperature, an intensive property
X is an extensive property which is result of heat transfer is

a. Q1-2 = 12 T dX
b. Q1-2 = 12 X dT
c. Q1-2 = 12 (1/T) dX
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Q1-2 = 1∫2 T dX Explanation: Heat transfer is also a path function like work transfer. The work involved in a thermodynamic process is give by the equation,W1-2 = 1∫2 P dVwhere,p is the pressure and V is the volume of the system.Whenever there is change in pressure, there will be displacement work. Therefore, pressure difference is a cause and the work transfer is the effect and the change in volume is a result. The quantity of the heat transfer can also be determined as work transfer. In heat transfer process, whenever there is temperature difference, heat transfer takes place and a change is certain extensive property takes place. Thus, temperature is the cause and heat transfer is the effect. Therefore, the heat flow can be determined by Q1-2 = 1∫2 T dX.

9)   The amount of heat required to raise a unit mass of substance through a unit rise in temperature is called as

a. heat capacity of a substance
b. specific heat of a substance
c. latent heat of a substance
d. none of the above
 Answer  Explanation  Related Ques ANSWER: specific heat of a substance Explanation: Specific heat of the substance is defined as the amount of heat required to raise a unit mass of substance through a unit rise in temperature. The symbol used for specific heat is 'c'.c = Q / (m . Δt) J/kg KWhere Q is the amount of heat in J, m is the mass of substance in kg, t is the temperature in K.For gases, if the process is at constant pressure then specific heat iscp. If the process is at constant volume, then it is cv. The product of mass (m) of the substance and specific heat (c) is heat capacity. The capital letters, C , Cp , Cp are used for heat capacity.

10)   The amount of heat transferred to convert unit mass of solid to vapour or vice versa is called as

a. latent heat of vaporization
b. latent heat of fusion
c. latent heat of sublimation
d. specific heat
 Answer  Explanation  Related Ques ANSWER: latent heat of sublimation Explanation: The amount of heat transfer required to cause a phase change in unit mass of a substance at constant volume and temperature is called as latent heat. There are three types of latent heat as there are three phases solid, liquid, gas or vapour. The amount of heat transfer required to melt unit mass into liquid or liquid into solid is the latent heat of fusion (lfu). The latent heat of vaporization (lvap) is the amount of heat transfer required to vaporise unit mass of liquid into vapour or vice versa. The latent heat of sublimation (lsub) is the amount of heat transfer required to convert unit mass of solid into vapour of vice versa.

11)   Which among the following statements are correct?
(1) Energy is an extensive property
(2) Specific energy is an extensive property
(3) Energy is a point function
(4) Heat capacity is an extensive property

a. Statement (1), (2) and (3)
b. Statement (1), (3) and (4)
c. Statement (2), (3) and (4)
d. Statement (1), (2), (3) and (4)
 Answer  Explanation  Related Ques ANSWER: Statement (1), (3) and (4) Explanation: We know that, when a system changes from state 1 to state 2, the change in internal energy (ΔE) of the state 2 is same as that of the state 1. Therefore value of internal energy of the system is independent of the path followed by the system. It has a fixed value along the path, therefore energy is the point function [statement (3) is correct]. But energy changes with mass of the body, therefore it is an extensive property [statement (1) is correct]. Specific energy is the energy of the system per unit mass of the system, therefore it will become intensive property [statement (2) is wrong]. Heat capacity is the product of specific heat and mass of the body. It depends on mass of the system, therefore heat capacity is an extensive property.

12)   A quasi-static process has main characteristics as it is

a. a stationary process
b. an infinitely slow process
c. a random process
d. a spontaneous process
 Answer  Explanation  Related Ques ANSWER: an infinitely slow process Explanation: Consider a system of gas exists in a cylinder. The piston consists of many very small pieces of weights. Initially system is in an equilibrium state. When the gas system is isolated, the weights on piston are removed one by one slowly, at any instant of upward travel of the piston. So every state passes through by the system will be in an equilibrium state. Thus the system passes through the locus of all equilibrium points. This infinitely slow system is a quasi-static process. If the same small weights are now placed slowly one by one on top of the piston then the process will reverse in the same manner.

13)   Match the following irreversibilities

(1) Mechanical irreversibility ------ (A) Refrigeration cycle
(2) Thermal irreversibility --------- (B) Forming of water by combination of Hydrogen and Oxygen
(3) Chemical irreversibility -------- (C) Free expansion of gas in a system
(4) External irreversibility --------- (D) Melting of ice cube under the sunlight

a. (1)-(A), (2)-(B), (3)-(C), (4)-(D)
b. (1)-(A), (2)-(D), (3)-(B), (4)-(C)
c. (1)-(C), (2)-(D), (3)-(A), (4)-(B)
d. (1)-(C), (2)-(D), (3)-(B), (4)-(A)
 Answer  Explanation  Related Ques ANSWER: (1)-(C), (2)-(D), (3)-(B), (4)-(A) Explanation: If the irreversibility is due to a finite pressure gradient, it is called as mechanical irreversibility. Thus, free expansion of gas in a system is the example of mechanical irreversibility. It the irreversibility is due to a finite temperature gradient, it is called as thermal irreversibility. Thus, melting of ice cube under the sunlight is the example of mechanical irreversibility. If the irreversibility is due to a finite concentration gradient or chemical reaction in the system, it is called as chemical irreversibility. Thus, forming of water by combination of Hydrogen and Oxygen is the example of mechanical irreversibility.In refrigeration cycle, irreversibility occurs due to temperature difference between the source and a working fluid that is refrigerant at heat supply and the temperature difference between the sink and the refrigerant at heat rejection.

14)   A cyclic heat engine operates between a source temperature of 927 oC and a sink temperature of 27 oC. What will be the maximum efficiency of the heat engine?

a. 100 %
b. 80 %
c. 75 %
d. 70 %
 Answer  Explanation  Related Ques ANSWER: 75 % Explanation: Heat engine is operated between the temperaturesT1 = 927 0C = 927 + 273 = 1200 K andT2 = 27 0C = 27 + 273 = 300 KThe maximum efficiency of a heat engine is given by,ηmax = 1 – (T2/T1)ηmax = 1 – (300/1200)ηmax = 0.75

15)   PMM2 is the machine which violates ___________

a. Kelvin-Planck statement
b. Clausius statement
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: both a. and b. Explanation: PMM2 (Perpetual Motion Machine of the Second Kind) is a hypothetical machine which violates the second law of thermodynamics. Kelvin-Planck as well as Clausius statement both represents the second law of thermodynamics. The Kelvin-Planck statement is related to heat engine whereas the Clausius statement is related to heat pump.If a machine violates one of the two statements then the other statement is always violated. Therefore, PMM2 is the machine which violates both Kelvin-Planck as well as Clausius statement of second law of thermodynamics.

16)   What is the equation for entropy of a system if two parts 1 and 2 having entropies S1 and S2 are considered in equilibrium?

a. S = S1 – S2
b. S = S1 + S2
c. S = (S1 + S2) / 2
d. S = √S1 S2
 Answer  Explanation  Related Ques ANSWER: S = S1 + S2 Explanation: No explanation is available for this question!

17)   Exergy is not conserved but destroyed in the process. What is the reason behind this?

a. reversibility
b. irreversibility
c. both reversibility and irreversibility
d. none of the above
 Answer  Explanation  Related Ques ANSWER: irreversibility Explanation: No explanation is available for this question!

18)   What does the exergy principle state?

a. The exergy of an isolated system can never decreases, but always increases
b. The exergy of an isolated system can never increases, but always decreases
c. The exergy of an isolated system can either increases or decreases
d. cannot say
 Answer  Explanation  Related Ques ANSWER: The exergy of an isolated system can never increases, but always decreases Explanation: No explanation is available for this question!

19)   People use electric energy to heat and light homes. What does it indicate?

a. People are destroying energy
b. People are creating energy
c. People are converting energy from more exergy value to less exergy value
d. People are converting energy from less exergy value to more exergy value
 Answer  Explanation  Related Ques ANSWER: People are converting energy from more exergy value to less exergy value Explanation: No explanation is available for this question!

20)   The ratio of minimum exergy which must be consumed to perform the task to the actual amount of energy consumed in performing the same task is called as

a. first law efficiency
b. second law efficiency
c. exergy efficiency
d. none of the above
 Answer  Explanation  Related Ques ANSWER: second law efficiency Explanation: No explanation is available for this question!

21)   The dryness (x) fraction of superheated steam is taken as

a. x= 0
b. x= 0.9
c. x= 0.999
d. x= 1
 Answer  Explanation  Related Ques ANSWER: x= 1 Explanation: No explanation is available for this question!

22)   What is a liquid, whose temperature is less than the saturation temperature at the given pressure, called?

a. compressed liquid
b. subcooled liquid
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: both a. and b. Explanation: No explanation is available for this question!

23)   What is the degree of subcooling?

a. the difference between saturation temperature of liquid and actual temperature of liquid
b. the difference between saturation temperature of vapour and actual temperature of liquid
c. the difference between saturation temperature of liquid and actual temperature of vapour
d. the difference between saturation temperature of vapour and actual temperature of vapour
 Answer  Explanation  Related Ques ANSWER: the difference between saturation temperature of liquid and actual temperature of liquid Explanation: No explanation is available for this question!

24)   Dalton's law of partial pressure states that

a. the total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of individual gases divided by number of gases mixed

b. the total pressure of a mixture of ideal gases is equal to the partial pressure of any individual gas in the mixture

c. the total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of individual gases

d. none of the above
 Answer  Explanation  Related Ques ANSWER: the total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of individual gases Explanation: No explanation is available for this question!

25)   What is the partial volume of a gas in a mixture?

a. volume occupied by a single gas alone of a mixture at the same temperature and pressure of the mixture
b. total volume of the mixture at a certain pressure and temperature divided number of gases mixed in the mixture
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: volume occupied by a single gas alone of a mixture at the same temperature and pressure of the mixture Explanation: No explanation is available for this question!

26)   The sum of partial volumes of all gases in a mixture is equal to

a. less than the total volume of the mixture
b. the total volume of the mixture
c. more than the total volume of the mixture
d. cannot predict
 Answer  Explanation  Related Ques ANSWER: the total volume of the mixture Explanation: No explanation is available for this question!

27)   In binary vapour cycle, the cycle which is operated in high pressure ratio is called as

a. bottoming cycle
b. topping cycle
c. upper cycle
d. pressure cycle
 Answer  Explanation  Related Ques ANSWER: topping cycle Explanation: No explanation is available for this question!

28)   What is the correct formula for brake efficiency of the turbine in vapour power cycle?
Where out flow is as following,Ideal output(Actual work given to turbine) ----> Internal losses ----> Internal output (Actual work produced by turbine turbine) ----> External losses -----> Brake output (Actual work at the shaft)

a. ηBrake = Brake output / Ideal output
b. ηBrake = Brake output / Internal output
c. ηBrake = Ideal output / Brake output
d. ηBrake = Internal output / Brake output
 Answer  Explanation  Related Ques ANSWER: ηBrake = Brake output / Ideal output Explanation: No explanation is available for this question!

29)   What is the relation between brake efficiency, internal efficiency and mechanical efficiency?

a. ηInternal = ηMech * ηBrake
b. ηMech = ηInternal * ηBrake
c. ηBrake = ηInternal * ηMech
d. none of the above
 Answer  Explanation  Related Ques ANSWER: ηBrake = ηInternal * ηMech Explanation: No explanation is available for this question!

30)   How is the COP of gas-refrigeration cycle compared with the COP of vapour compression cycle, for the same capacity?

a. the COP of gas-refrigeration cycle is lower than the COP of vapour compression cycle, for the same capacity
b. the COP of gas-refrigeration cycle is higher than the COP of vapour compression cycle, for the same capacity
c. the COP of gas-refrigeration cycle is same as the COP of vapour compression cycle
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the COP of gas-refrigeration cycle is lower than the COP of vapour compression cycle, for the same capacity Explanation: No explanation is available for this question!

31)   The gas-refrigeration system is

a. more heavy and bulky than the vapour compression cycle
b. less heavy and bulky than the vapour compression cycle
c. same in construction with the vapour compression cycle
d. none of the above
 Answer  Explanation  Related Ques ANSWER: less heavy and bulky than the vapour compression cycle Explanation: No explanation is available for this question!

32)   What is the perfect condition for dehumidification of air?

a. air is heated above its dew point temperature
b. air is cooled up to its dew point temperature
c. air is heated below its dew point temperature
d. air is cooled below its dew point temperature
 Answer  Explanation  Related Ques ANSWER: air is cooled below its dew point temperature Explanation: No explanation is available for this question!

33)   At 100% relative humidity, the wet bulb temperature is

a. lower than the dew point temperature
b. higher than the dew point temperature
c. equal to the dew point temperature
d. none of the above
 Answer  Explanation  Related Ques ANSWER: equal to the dew point temperature Explanation: No explanation is available for this question!

34)   The dew point temperature is less than the wet bulb temperature for

a. saturated air
b. unsaturated air
c. both saturated and unsaturated air
d. none of the above
 Answer  Explanation  Related Ques ANSWER: unsaturated air Explanation: No explanation is available for this question!

35)   When,
H1 = Total heat of air entering the coil (heating or cooling)
H2 = Total heat of air leaving the coil (heating or cooling)
H3 = Total heat of air at the end of the process (humidification or dehumidification)
then, the sensible heat factor (H2 – H1) / (H3 – H1) represents the process of

a. cooling and humidification
b. cooling and dehumidification
c. heating and humidification
d. heating and dehumidification
 Answer  Explanation  Related Ques ANSWER: heating and humidification Explanation: No explanation is available for this question!

36)   When the rate of evaporation of water is zero, the relative humidity of the air is

a. 0%
b. 100%
c. 50%
d. unpredictable
 Answer  Explanation  Related Ques ANSWER: 100% Explanation: No explanation is available for this question!

37)   What is the pH value of water permissible for boiler?

a. 0
b. 7
c. slightly less than 7
d. slightly more than 7
 Answer  Explanation  Related Ques ANSWER: slightly more than 7 Explanation: No explanation is available for this question!

38)   The formation of scale boiler leads to

a. decrease in efficiency of boiler
b. increase in efficiency of boiler
c. increase in heat transfer
d. decrease in maintenance of boiler
 Answer  Explanation  Related Ques ANSWER: decrease in efficiency of boiler Explanation: No explanation is available for this question!