These 40 MCQs cover a wide range of topics within Engineering Thermodynamics, including fundamental laws, processes, cycles, and practical applications in systems like refrigeration, engines, and compressors. They are designed to test knowledge in both academic and practical contexts within the field.
1. What is the first law of thermodynamics?
a) Energy can neither be created nor destroyed
b) Entropy of a system always increases
c) Heat transfer is equal to work done
d) Temperature remains constant during a thermodynamic process
Answer:
a) Energy can neither be created nor destroyed
Explanation:
The first law of thermodynamics, also known as the law of energy conservation, states that energy can neither be created nor destroyed, only transferred or transformed.
2. What does the second law of thermodynamics state?
a) Energy transfer has no direction
b) Entropy of an isolated system always increases
c) Total energy of an isolated system is constant
d) Pressure and volume of a gas are inversely proportional
Answer:
b) Entropy of an isolated system always increases
Explanation:
The second law of thermodynamics states that the entropy of an isolated system always increases over time, leading to the irreversible nature of natural processes.
3. What is entropy?
a) A measure of pressure exerted by a gas
b) A measure of a system's thermal energy per unit temperature that is unavailable for doing work
c) A measure of total heat content of a system
d) A measure of the volume of a system
Answer:
b) A measure of a system's thermal energy per unit temperature that is unavailable for doing work
Explanation:
Entropy is a measure of disorder or randomness in a system and also represents the amount of thermal energy in a system that cannot be used to do work.
4. In a thermodynamic process, if the system does work on the surroundings, the work is considered:
a) Positive
b) Negative
c) Zero
d) Constant
Answer:
b) Negative
Explanation:
In thermodynamics, work done by the system on the surroundings is considered negative, as energy is being transferred out of the system.
5. What is an isothermal process?
a) A process that occurs at constant temperature
b) A process that occurs at constant pressure
c) A process that occurs without heat transfer
d) A process that occurs at constant volume
Answer:
a) A process that occurs at constant temperature
Explanation:
An isothermal process is a thermodynamic process in which the temperature of the system remains constant while other properties may change.
6. What is the Carnot cycle?
a) A cycle that describes the functioning of all heat engines
b) A theoretical thermodynamic cycle with maximum efficiency
c) A cycle that represents all refrigeration processes
d) A cycle used in all combustion engines
Answer:
b) A theoretical thermodynamic cycle with maximum efficiency
Explanation:
The Carnot cycle is a theoretical thermodynamic cycle proposed by Nicolas Léonard Sadi Carnot. It represents the upper limit on the efficiency that any classical thermodynamic engine can achieve.
7. What is the function of a compressor in a refrigeration cycle?
a) To absorb heat from the environment
b) To expel heat to the environment
c) To increase the pressure of the refrigerant
d) To decrease the temperature of the refrigerant
Answer:
c) To increase the pressure of the refrigerant
Explanation:
In a refrigeration cycle, the compressor's function is to increase the pressure of the refrigerant, which raises its temperature and enables heat rejection in the condenser.
8. What is a heat exchanger?
a) A device that converts heat into work
b) A device that exclusively radiates heat
c) A device used for transferring heat between two or more fluids
d) A device used for measuring temperature
Answer:
c) A device used for transferring heat between two or more fluids
Explanation:
A heat exchanger is a device used to transfer heat between two or more fluids (like liquids, gases, or vapors) without them mixing together.
9. In an ideal gas, what is the relationship between pressure and temperature during an isobaric process?
a) They are inversely proportional
b) They are directly proportional
c) They are unrelated
d) They are exponentially related
Answer:
b) They are directly proportional
Explanation:
In an isobaric process (constant pressure), the pressure and temperature of an ideal gas are directly proportional, as stated by Gay-Lussac's law.
10. What principle does a jet engine operate on?
a) Bernoulli's principle
b) Newton's third law of motion
c) Pascal's law
d) Boyle's law
Answer:
b) Newton's third law of motion
Explanation:
Jet engines operate based on Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. The engine expels gas at high speed backward, which propels the aircraft forward.
11. What is the primary function of a condenser in a steam power plant?
a) To convert steam into water
b) To generate steam
c) To superheat steam
d) To increase steam pressure
Answer:
a) To convert steam into water
Explanation:
In a steam power plant, the condenser's primary function is to condense exhaust steam from the turbine into water so it can be reused in the boiler.
12. What is specific heat capacity?
a) The amount of heat required to raise the temperature of a unit mass by one degree
b) The total heat content in a substance
c) The heat required to change the state of a substance
d) The heat transfer rate of a substance
Answer:
a) The amount of heat required to raise the temperature of a unit mass by one degree
Explanation:
Specific heat capacity is a property that indicates the amount of heat required to change the temperature of a unit mass of a substance by one degree Celsius or Kelvin.
13. What is the zeroth law of thermodynamics?
a) It defines temperature
b) It introduces the concept of entropy
c) It states that if two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other
d) It describes the conservation of energy
Answer:
c) It states that if two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other
Explanation:
The zeroth law of thermodynamics establishes the basis for the concept of temperature. It states that if two thermodynamic systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.
14. What is a thermodynamic cycle?
a) A single process in a thermodynamic system
b) A series of processes after which the system returns to its initial state
c) A continuous process that increases system entropy
d) The process of converting heat into work
Answer:
b) A series of processes after which the system returns to its initial state
Explanation:
A thermodynamic cycle consists of a series of thermodynamic processes that occur in a certain sequence so that the system returns to its original state at the end of the cycle.
15. What is the Kelvin-Planck statement of the second law of thermodynamics?
a) It is impossible for a process to have as its sole result the transfer of heat from a cooler to a hotter body
b) It is impossible for a heat engine to operate in a cycle that produces no other effect than the absorption of heat from a reservoir and the performance of an equivalent amount of work
c) Efficiency of a cyclic process can never be 100%
d) The entropy of an isolated system always increases
Answer:
b) It is impossible for a heat engine to operate in a cycle that produces no other effect than the absorption of heat from a reservoir and the performance of an equivalent amount of work
Explanation:
The Kelvin-Planck statement of the second law of thermodynamics states that it is impossible to construct an engine that, operating in a cycle, will produce no effect other than the extraction of heat from a heat reservoir and the performance of an equivalent amount of work.
16. What is the primary purpose of a nozzle in a thermodynamic system?
a) To increase pressure
b) To reduce temperature
c) To increase velocity
d) To decrease velocity
Answer:
c) To increase velocity
Explanation:
In thermodynamics, a nozzle is used to increase the velocity of a fluid at the expense of its pressure. Nozzles convert thermal energy into kinetic energy.
17. The process of absorbing heat at constant temperature and transforming it into work is characteristic of:
a) An isothermal process
b) An adiabatic process
c) A polytropic process
d) A throttling process
Answer:
a) An isothermal process
Explanation:
An isothermal process is characterized by constant temperature. In such a process, the system can absorb or release heat while doing work without changing its temperature.
18. The Clausius statement of the second law of thermodynamics asserts that:
a) It is impossible to construct a device that operates in a cycle and produces no other effect than the transfer of heat from a cooler body to a hotter body
b) The entropy of the universe always increases
c) Work can be fully converted into heat
d) Heat cannot be converted entirely into work
Answer:
a) It is impossible to construct a device that operates in a cycle and produces no other effect than the transfer of heat from a cooler body to a hotter body
Explanation:
The Clausius statement of the second law of thermodynamics states that it is impossible to construct a device that, operating in a cycle, will produce no effect other than the transfer of heat from a lower-temperature body to a higher-temperature body.
19. In thermodynamics, what does the term "adiabatic process" mean?
a) A process in which heat is neither added nor removed from the system
b) A process in which pressure remains constant
c) A process in which volume remains constant
d) A process in which temperature remains constant
Answer:
a) A process in which heat is neither added nor removed from the system
Explanation:
An adiabatic process is a thermodynamic process in which no heat is transferred to or from the system, meaning the system is perfectly insulated.
20. What is the critical point in a phase diagram?
a) The point where solid and liquid phases coexist
b) The point where all three phases (solid, liquid, and gas) coexist
c) The point beyond which distinct liquid and gas phases do not exist
d) The lowest temperature at which a substance can exist in liquid form
Answer:
c) The point beyond which distinct liquid and gas phases do not exist
Explanation:
The critical point on a phase diagram is the end point of the phase equilibrium curve, beyond which the liquid and gas phases become indistinguishable from each other.
21. What does a Mollier diagram represent?
a) Pressure-Volume relationships
b) Temperature-Entropy relationships
c) Enthalpy-Entropy relationships
d) Temperature-Volume relationships
Answer:
c) Enthalpy-Entropy relationships
Explanation:
A Mollier diagram, or H-S chart, represents the relationship between enthalpy (H) and entropy (S) of a substance, commonly used for working fluids in a thermodynamic cycle.
22. The efficiency of a Carnot cycle depends on:
a) The working substance used in the cycle
b) The sizes of the heat reservoirs
c) The temperatures of the hot and cold reservoirs
d) The pressure at which the cycle operates
Answer:
c) The temperatures of the hot and cold reservoirs
Explanation:
The efficiency of a Carnot cycle is dependent solely on the temperatures of the hot and cold reservoirs and is independent of the working substance or the type of heat engine used.
23. What is the primary purpose of regenerative feed heating in steam power plants?
a) To reduce fuel consumption
b) To increase the temperature of the feedwater
c) To improve the overall efficiency of the power plant
d) Both b and c
Answer:
d) Both b and c
Explanation:
Regenerative feed heating in steam power plants preheats the feedwater using steam extracted from the turbine, which improves the overall efficiency and reduces fuel consumption by reducing the heat addition required in the boiler.
24. In a Rankine cycle, the process of converting water into steam takes place in the:
a) Turbine
b) Condenser
c) Boiler
d) Pump
Answer:
c) Boiler
Explanation:
In the Rankine cycle, which is a common steam cycle for power generation, the conversion of water into steam occurs in the boiler.
25. What is the primary distinction between heat and temperature?
a) Heat is a form of energy, while temperature is a measure of energy
b) Heat is a measure of the hotness or coldness of an object, while temperature is the flow of energy
c) Heat and temperature are the same
d) Heat is measured in Joules, while temperature is measured in Pascals
Answer:
a) Heat is a form of energy, while temperature is a measure of energy
Explanation:
Heat is a form of energy transfer between systems due to a temperature difference, while temperature is a measure of the average kinetic energy of particles in a substance.
26. What is the specific volume of a substance?
a) The volume occupied by a unit mass of the substance
b) The total volume of the substance
c) The ratio of volume to pressure of the substance
d) The change in volume with temperature
Answer:
a) The volume occupied by a unit mass of the substance
Explanation:
Specific volume is a property of materials, defined as the volume occupied by a unit mass of a substance. It is the reciprocal of density.
27. In thermodynamics, a 'closed system' is defined as:
a) A system that exchanges neither mass nor energy with its surroundings
b) A system that exchanges energy but not mass with its surroundings
c) A system that exchanges both mass and energy with its surroundings
d) A system isolated from its surroundings
Answer:
b) A system that exchanges energy but not mass with its surroundings
Explanation:
A closed system in thermodynamics is one where energy in the form of heat or work may cross the boundary, but mass does not.
28. What is the heat transfer process that does not require a medium?
a) Conduction
b) Convection
c) Radiation
d) Advection
Answer:
c) Radiation
Explanation:
Radiation is a mode of heat transfer that does not require any medium. It involves the transfer of energy by electromagnetic waves, such as the heat from the sun.
29. What is the primary function of a pump in a hydraulic system?
a) To regulate temperature
b) To control fluid flow rate
c) To increase fluid pressure
d) To decrease fluid volume
Answer:
c) To increase fluid pressure
Explanation:
In a hydraulic system, the pump's primary function is to increase the pressure of the fluid, which is then used to do work in the system, such as moving pistons, gears, or rotors.
30. In the context of refrigeration, what is subcooling?
a) Cooling a liquid below its boiling point at a given pressure
b) Cooling a vapor below its condensation point
c) Heating a liquid above its boiling point
d) Decreasing the temperature of the refrigerant in the evaporator
Answer:
a) Cooling a liquid below its boiling point at a given pressure
Explanation:
Subcooling in refrigeration refers to the process of cooling a liquid refrigerant below its saturation temperature (boiling point) at a given pressure, typically after it leaves the condenser.
31. What is the difference between an isobaric and an isochoric process?
a) An isobaric process occurs at constant pressure, while an isochoric process occurs at constant volume
b) An isobaric process occurs at constant volume, while an isochoric process occurs at constant pressure
c) An isobaric process involves no heat transfer, while an isochoric process involves heat transfer
d) There is no difference; they are the same
Answer:
a) An isobaric process occurs at constant pressure, while an isochoric process occurs at constant volume
Explanation:
In an isobaric process, the pressure remains constant while the volume may change. In an isochoric process, the volume remains constant, but the pressure may change.
32. The Stefan-Boltzmann law relates to:
a) Heat transfer by conduction
b) Heat transfer by convection
c) Heat transfer by radiation
d) Work done in an adiabatic process
Answer:
c) Heat transfer by radiation
Explanation:
The Stefan-Boltzmann law relates to heat transfer by radiation, stating that the total energy radiated per unit surface area of a black body is directly proportional to the fourth power of the black body's temperature.
33. What is a psychrometric chart used for?
a) Analyzing combustion processes
b) Measuring pressure in a system
c) Analyzing properties of moist air
d) Determining the efficiency of a heat engine
Answer:
c) Analyzing properties of moist air
Explanation:
A psychrometric chart is a graphical representation of the thermodynamic properties of moist air, used in air conditioning and drying applications.
34. What is the function of a throttle valve in a vapor compression refrigeration cycle?
a) To compress the refrigerant
b) To increase the temperature of the refrigerant
c) To expand and reduce the pressure of the refrigerant
d) To condense the refrigerant vapor
Answer:
c) To expand and reduce the pressure of the refrigerant
Explanation:
A throttle valve in a refrigeration cycle is used to expand the refrigerant, reducing its pressure and temperature before it enters the evaporator.
35. What does COP stand for in refrigeration and heat pump systems?
a) Coefficient of Performance
b) Coefficient of Pressure
c) Constant Operating Pressure
d) Cooling Operation Potential
Answer:
a) Coefficient of Performance
Explanation:
COP, or Coefficient of Performance, is a measure of efficiency used for heat pumps and refrigeration systems. It is the ratio of cooling or heating provided to electrical energy consumed.
36. What is a reversible process in thermodynamics?
a) A process that can be reversed without leaving any trace on the surroundings
b) A process that can be reversed only under ideal conditions
c) A process that cannot be reversed
d) A process that occurs spontaneously
Answer:
a) A process that can be reversed without leaving any trace on the surroundings
Explanation:
A reversible process in thermodynamics is an idealized process that can be reversed without any change in both the system and the surroundings. In reality, all natural processes are irreversible.
37. What is the primary characteristic of a superheated vapor?
a) It is at a temperature below its saturation temperature
b) It is at a temperature and pressure where liquid and vapor coexist
c) It is at a temperature above its saturation temperature
d) It is in a compressed liquid state
Answer:
c) It is at a temperature above its saturation temperature
Explanation:
A superheated vapor is a state where the vapor is at a temperature higher than the saturation temperature for a given pressure, meaning it is not about to condense.
38. What is meant by 'dryness fraction' in the context of steam?
a) The fraction of liquid in the mixture
b) The fraction of vapor in the mixture
c) The temperature of the steam
d) The pressure of the steam
Answer:
b) The fraction of vapor in the mixture
Explanation:
The dryness fraction is a term used in steam thermodynamics to describe the proportion of vapor in a wet steam mixture. It indicates the quality of steam, with a higher dryness fraction meaning more vapor and less liquid.
39. In a heat engine, what is the typical role of the working fluid?
a) To provide lubrication to moving parts
b) To absorb heat from the surroundings
c) To convert heat energy into mechanical work
d) To regulate the temperature inside the engine
Answer:
c) To convert heat energy into mechanical work
Explanation:
In a heat engine, the working fluid plays a crucial role in converting heat energy into mechanical work. It absorbs heat, undergoes an expansion or phase change, and does work on the mechanical components of the engine.
40. What is the principle of operation for a centrifugal compressor?
a) Increasing pressure by decreasing the volume
b) Increasing the velocity of the fluid, then converting kinetic energy to pressure
c) Compressing the fluid with a piston
d) Reducing the temperature to increase pressure
Answer:
b) Increasing the velocity of the fluid, then converting kinetic energy to pressure
Explanation:
A centrifugal compressor works by increasing the velocity of the fluid (usually a gas) using a rotating impeller. This high-velocity fluid is then passed through a diffuser where its kinetic energy is converted into pressure, resulting in compressed gas at the outlet.