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### Thermodynamics important questions

Question No 1 :
The following are examples of some intensive and extensive properties :
1. Pressure
2. Temperature
3. Volume
4. Velocity
5. Electronic charge
6. Magnetisation
7. Viscosity
8. Potential energy
Which one of the following sets gives the correct combinations of Intensive and Extensive properties?
Option A : Intensive - 1 2 3 4 Extensive - 5 6 7 8
Option B : Intensive - 1 3 5 7 Extensive - 2 4 6 8
Option C : Intensive - 1 2 4 7 Extensive - 3 5 6 8
Option D : Intensive - 2 3 6 8 Extensive - 1 4 5 7
Explanation :
Intensive properties : Independent of mass
Extensive properties : Dependent of mass

Question No 2 :
In an isothermal process, internal energy?
Option A: Increases
Option B: Decreases
Option C: Remain constant
Explanation: Decreases

Question No 3 :
A reversible process?
Option A: Must pass through a continuous series of equilibrium states
Option B: Leaves no history of the events in surroundings
Option C: Must pass through the same states on the reversed path as on the forward path
Option D: All of these
Explanation: All of the above

Question No 4 :
The specific heat of water with rising of temperature?
Option A: Increases
Option B: Decreases
Option C: First decreases to a minimum then increases
Option D: Remain constant
Explanation: Decrease to a minimum first then increase

Question No 5 :
When two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. This statement is :
Option A: Zeroth law of thermodynamics
Option B: First law of thermodynamics
Option C: Second law of thermodynamics
Option D: None of the above
Explanation: This is the statement of the zeroth law of thermodynamics

Question No 6 :
Kelvin-Plank's law deals with?
Option A: Conversion of work into heat
Option B: Conversion of heat into work
Option C: Conversion of work
Option D: Conversion of heat
Explanation: Conversion of heat into work

Question No 7 :
According to the kinetic theory of gases, at absolute zero?
Option A: Specific heat of molecules reduces to zero
Option B: Volume of gas reduce to zero
Option C: Kinetic energy of molecules reduces to zero
Option D: Pressure of gas reduces to zero
Explanation: Kinetic energy of molecules reduces to zero

Question No 8 :
In a throttling process?
Option A : W = 0
Option B : H = 0
Option C : E = 0
Option D : All of the above
Explanation : At throttling all W, H, E = 0

Question No 9 :
In all reversible process, the entropy of the universe?
Option A: Increases
Option B: Decreases
Option C: Remains the same
Option D: None of the above
Explanation: Increases

Question No 10 :
Efficiency of Carnot cycle is given by :
Option A : T1 + T2 / T1
Option B : T1 - T2 / T1
Option C : T1 / T1 + T2
Option D : T1 / T1 - T2
Explanation : T1 - T2 / T1

Question No 11 :
The Carnot cycle consists of two reversible adiabatic processes and
Option A: Two reversible isothermal processes
Option B: Two reversible constant pressure processes
Option C: Two reversible constant volume processes
Option D: One reversible constant pressure processes
Explanation: Two reversible isothermal processes

Question No 12 :
Carnot cycle has maximum efficiency for?
Option A : Petrol engine
Option B : Diesel engine
Option C : Reversible engine
Option D : Irreversible engine
Explanation : Reversible engine

Question No 13 :
In the Carnot cycle, the algebraic sum of the entropy changes for the cycle is?
Option A: Positive
Option B: Negative
Option C: Zero
Option D: None of the above
Explanation: Zero

Question No 14 :
In the Carnot cycle, the process carried at extremely slow speed is
Option A: Isothermal compression
Option D: All of these
Explanation: All are extremely slow speed processes

Question No 15 :
Control volume refers to a
Option A: Specific mass
Option B: Fixed region in the space
Option C: Closed system
Option D: NONE
Explanation: Fixed region in the space

Question No 16 :
The internal energy of a perfect gas depends upon
Option A: Temperature only
Option B: Temperature and pressure
Option C: Temperature, pressure and specific heats
Option D: NONE
Explanation: Temperature only

Question No 17 :
Joule Thomson coefficient for an ideal gas having equation pV=RT is
Option A: Zero
Option B: 0.5
Option C: Unity
Option D: Infinite
Explanation: Zero

Question No 18 :
The temperature of a gas is a measure of
Option A: Average distance between gas molecules
Option B: Average kinetic energy of gas molecules
Option C: Average potential energy of gas molecules
Option D: NONE
Explanation: Average kinetic energy of gas molecules

Question No 19 :
A gas, which obeys kinetic theory perfectly is
Option A: Pure gas
Option B: Real gas
Option C: Perfect gas
Option D: All of these
Explanation: Real gas

Question No 20 :
The temperature at which, the volume of a gas becomes zero, is called
Option A: Absolute temperature
Option B: Absolute zero temperature
Option C: Absolute scale of temperature
Option D: NONE of these
Explanation: Absolute zero temperature

Question No 21 :
The absolute zero pressure exists
Option A: At sea level
Option B: At -273 K
Option C: At vacuum condition
Option D: When the molecular momentum of the system becomes zero
Explanation: When the molecular momentum of the system becomes zero

Question No 22 :
Specific heat of gas, Cp = Cv, at
Option A: Absolute zero
Option B: Critical temperature
Option C: Triple point
Option D: All temperatures
Explanation: Absolute zero

Question No 23 :
The gas constant R is equal to the
Option A: Sum of two specific heats
Option B: Difference of two specific heats
Option C: Product of two specific heats
Option D: Ratio of two specific heat
Explanation: Difference of two specific heats

Question No 24 :
Triple point
Option A: Occurs in a mixture of two or more gases
Option B: In the point, where three phases exist together
Option C: Occurs in sublimation
Option D: None of the above
Explanation: In the point, where three phases exist together

Question No 25 :
For a pure substance at its triple point, the number of degrees of freedom is
Option A: 0
Option B: 1
Option C: 2
Option D: None of these
Explanation: Zero
Consider a system consisting of pure gas, say A. It is, evidently, a one-component, one phase system. The two variable required to be specified will be temperature and pressure. The composition will remain invariable A. The degree of freedom will be 2 if the system will be bivariant. One component system having two phases called mono variant and three phases coexist defines the system completely, therefore, is said to be non-variant or invariant or degree of freedom is zero.

Question No 26 :
The efficiency of a Rankine cycle
Option A: Increases with decreasing temperature of heat rejection
Option B: Decreases with decreasing temperature of heat rejection
Option C: Decreases with increasing temperature of heat rejection
Option D: None of the above
Explanation: Increase with decreasing temperature and decrease with increasing temperature of heat rejection.

Question No 27 :
Rankine cycle efficiency for a power plant is 29%. The Carnot cycle efficiency will be
Option A: Less
Option B: More
Option C: Equal
Option D: NONE of the above
Explanation: Carnot cycle efficiency is more than the Rankine cycle for the power plant.

Question No 28 :
The ideal efficiency of a simple gas turbine cycle depends upon
Option A: Pressure ratio
Option B: Cut-off ratio
Option C: Both A & B
Option D: None of the above
Explanation: Pressure ratio

Question No 29 :

A system is said to be consisting of a pure substance when
Option A: It is homogeneous in composition
Option B: It is homogeneous and invariable in chemical aggregation
Option C: It has only one phase
Option D: It has more than one phase
Explanation: It is homogeneous and invariable in chemical aggregation
A pure substance is one which is
Homogeneous in composition
Homogeneous in chemical aggregation
Invariable in chemical aggregation

Question No 30 :
At its critical point, any substance will
Option A: Exist all the three phases simultaneously
Option B: Change directly from solid to vapour
Option C: Lose phase distinction between liquid and vapour
Option D: Behave as an ideal gas
Explanation: Lose phase distinction between liquid and vapour