# Introduction to Thermodynamics - Mechanical Engineering (MCQ) questions and answers

1)   Homogeneous system

a. consists any one phase among solid, liquid and gas
b. consists only solid phase not liquid and gas
c. consists all three phases at particular temperature
d. none of the above
 Answer  Explanation ANSWER: consists any one phase among solid, liquid and gas Explanation: A quantity of matter homogeneous throughout in chemical composition and physical structure is called as a phase. Every substance can exist in any one or more of three phases like solid, liquid or gas. A system consisting of a single phase is called as homogeneous system, and a substance which consists of more than one phase is called as heterogeneous.

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 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 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)   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 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.

5)   Quasi-static process

a. is infinitely slow process
b. experiences thermodynamic equilibrium at every small point on its path
c. reversible process
d. all of the above
 Answer  Explanation ANSWER: all of the above 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.

6)   A system will be in a state of thermodynamic equilibrium, if it undergoes.

a. mechanical equilibrium
b. chemical equilibrium
c. thermal equilibrium
d. all of the above
 Answer  Explanation ANSWER: all of the above Explanation: When a system does not have any unbalanced force within itself and also between the system and its surrounding then the system is in the mechanical equilibrium. When there is no chemical reaction or transfer of matter from one system to surrounding or vice versa then the system is said to be considered as chemical equilibrium. When there is no transfer of heat from one part to another when system and surrounding are distinguished by a diathermic wall (the wall which allows heat to flow) then the system is said to be in thermal equilibrium. A system will be in a state of thermodynamic equilibrium when it undergoes all there equilibriums.

7)   Macroscopic thermodynamics ______

a. is concerned with the effects of action of many molecules in matter
b. results can be derived from microscopic study of matter
c. is not concerned with the events occurring at the molecular level
d. all of the above
 Answer  Explanation ANSWER: all of the above Explanation: Macroscopic and microscopic are the two point of views through which the behavior of a matter can be studied. In macroscopic point of view, the specific quantity of matter is considered. The behavior of the matter at the molecular level is not considered. In microscopic point of view, the behavior of the matter is described by summing up the behavior of each molecule.

8)   Which among the following is an intensive property of a system?

a. Volume
b. Energy
c. Pressure
d. all of the above
 Answer  Explanation ANSWER: Pressure Explanation: Intensive properties are independent of mass in a system and pressure does not depend upon mass in the system. Pressure, temperature etc. are some of the examples of intensive properties.

9)   The properties of a system whose values depend upon mass of the system are called as

a. intensive properties
b. extensive properties
c. dependent properties
d. massive properties
 Answer  Explanation ANSWER: extensive properties Explanation: Extensive properties depend upon mass in the system whereas intensive properties are independent of mass of the system. Volume, energy etc. are some of the examples of extensive properties. They are dependent upon mass of the system.

10)   The energy of an isolated system

a. is always decreasing
b. is always constant
c. is always increasing
d. none of the above
 Answer  Explanation ANSWER: is always constant Explanation: The system in which both the mass as well as energy cannot be transferred between system and its surrounding is called as isolated system. As the energy can neither be transmitted nor be absorbed, the total energy of an isolated system is always constant.