Thermodynamics — Set 3
Physics · ऊष्मागतिकी · Questions 21–30 of 40
A thermodynamic system that can exchange both mass and energy with its surroundings is called what?
Correct Answer: D. Open system
An open system allows both mass and energy to cross its boundary. Flowing fluids in turbines and compressors are common examples. A closed system does not allow mass transfer across the boundary.
A thermodynamic system that can exchange energy but not mass with its surroundings is called what?
Correct Answer: A. Closed system
A closed system can exchange energy with the surroundings but does not exchange mass. Heat and work may cross the boundary of a closed system. A sealed piston-cylinder containing gas is a common example.
A thermodynamic system that exchanges neither mass nor energy with its surroundings is called what?
Correct Answer: A. Isolated system
An isolated system does not exchange mass or energy with the surroundings. It is an idealization used to apply the second law simply. A perfectly insulated and sealed container is an approximate example.
Which of the following is an intensive property?
Correct Answer: A. Pressure
Pressure does not depend on how much substance is present, so it is intensive. Intensive properties remain the same for a system and its smaller parts. Mass and volume are extensive properties because they scale with size.
Which of the following is an extensive property?
Correct Answer: C. Volume
Volume depends on the amount of matter in the system, so it is extensive. If you combine two identical systems, the total volume adds up. Temperature and pressure do not add in this way.
Which quantity is generally treated as a path function in thermodynamics?
Correct Answer: C. Heat
Heat depends on the path taken during a process, so it is a path function. It is not a property stored as a fixed value in the state. Work is also a path-dependent quantity.
In an isochoric (constant volume) process, what is the work done by the gas?
Correct Answer: B. It is zero
Work done in a quasi-static process is W = ∫ P dV. In an isochoric process, volume does not change, so dV = 0. Therefore the work done is zero.
On a P-V diagram, the work done by a gas during a process is represented by what?
Correct Answer: B. The slope of the curve
In a P-V diagram, work is calculated as W = ∫ P dV. Graphically, this corresponds to the area under the process curve. The sign depends on whether the gas expands or is compressed.
According to Carnot’s theorem, which engine has the maximum possible efficiency between two given reservoirs?
Correct Answer: C. A reversible engine
Carnot’s theorem states that no engine can be more efficient than a reversible engine operating between the same temperatures. A Carnot engine is an ideal reversible engine. This sets an upper limit for all real heat engines.
A perpetual motion machine of the second kind would violate which law of thermodynamics?
Correct Answer: D. Second law
A perpetual motion machine of the second kind would convert heat from a single reservoir entirely into work. This directly contradicts the Kelvin-Planck statement of the second law. The first law is about energy conservation, not direction of processes.