Test: Basic Concept - 2 - Mechanical Engineering MCQ

Microscopic properties of thermodynamic systems provide critical insights into the behaviour and characteristics of matter. Understanding these properties involves several key points:

• Knowledge of matter's structure is crucial. It helps in understanding how particles interact and behave.
• Only a limited number of variables are necessary to define the state of a system, making analysis manageable.
• Contrary to some beliefs, the values of these variables can be measured with the right tools and techniques.
• Statistical averaging is used to predict the behaviour of individual particles, allowing for accurate predictions of system behaviour.

The correct statement discusses the nature of system boundaries in thermodynamics. Here are the key points:

• System Boundaries: These can change size; they are not fixed.
• Collapsible and Expandable: This means the boundaries can contract or expand based on the system's conditions.
• Types of Systems: Understanding system types is critical—open, closed, and isolated systems.

In contrast to the other options:

• Temperature: This is an intensive property, meaning it does not depend on the amount of substance present.
• Mass in Open Systems: Mass can change due to the exchange of matter with the surroundings.
• Isolated Systems: These do not allow any exchange of energy or matter, contradicting the notion of allowing heat exchange.

Open thermodynamic systems allow both matter and energy to cross their boundaries. Here are characteristics of such systems:

• Manual ice cream freezer: This is a closed system as it doesn't allow matter to enter or exit while freezing.
• Centrifugal pump: This is an open system because it moves fluid into and out of the pump, transferring energy and matter.
• Pressure cooker: This is a closed system because it retains steam and does not allow matter to escape.
• Bomb calorimeter: This is also a closed system, designed to measure heat transfer without matter exchange.

Among these options, the centrifugal pump is the best example of an open thermodynamic system.

A thermodynamic system is considered isolated when there is no transfer of energy or mass with its surroundings. This means:

• There is no energy transfer in the form of heat or work.
• There is no mass transfer, meaning no particles enter or exit the system.
• The system's internal energy remains constant.
• Entropy change, which measures disorder or randomness, is also zero.

In summary, an isolated system does not interact with its environment, ensuring stability in its energy and mass properties.

A control volume is a defined space used in engineering and physics to analyse the behaviour of fluids and energy. It is crucial for understanding various processes in thermodynamics and fluid mechanics.

• A control volume can be described as a fixed region in space.
• It allows for the exchange of mass, heat, and work across its boundaries.
• This concept is essential for analysing systems where these exchanges occur, such as engines and refrigerators.
• By isolating a control volume, we can apply the principles of conservation of mass, energy, and momentum.

In summary, a control volume is a valuable tool for engineers and scientists to study and model physical systems effectively.

Correct Answer :- d

Explanation : A thermodynamic system is a quantity of matter of fixed identity, around which we can draw a boundary The boundaries may be fixed or moveable. Work or heat can be transferred across the system boundary. Everything outside the boundary is the surroundings.

When working with devices such as engines it is often useful to define the system to be an identifiable volume with flow in and out. This is termed a control volume.

A closed system is a special class of system with boundaries that matter cannot cross. Hence the principle of the conservation of mass is automatically satisfied whenever we employ a closed system analysis. This type of system is sometimes termed a control mass.

The concept of continuum loses validity when the mean free path of the molecules approaches the order of magnitude of the dimension of the vessel. So, in highly rarefied gases the concept of continuum loses its validity.

A heterogeneous system consists of distinct components that can be physically separated. Here are some examples:

• Atmospheric air: Contains various gases like nitrogen, oxygen, and carbon dioxide, each identifiable.
• Mixture of hydrogen and oxygen: These gases do not chemically combine in a mixture.
• Cooling fluid in a radiator: Often includes a combination of water and antifreeze, maintaining distinct properties.
• Mixture of ice, water, and steam: This is a classic example of a heterogeneous system, as it contains solid, liquid, and gas phases existing simultaneously.

Among these, the mixture of ice, water, and steam is the most illustrative example of a heterogeneous system, showcasing different states of matter coexisting together.

Concept:

Properties

All measurable characteristics of a system are known as properties.

Eg. Pressure, volume, temperature, etc.

There are two types of properties:

Extensive property

• Those properties which depend on mass are known as extensive properties.
• Examples are volume, energy, enthalpy, entropy etc.

Intensive property

• Those properties which don't depend on mass are known as intensive properties.
• Examples are pressure, temperature, density, viscosity.