Test: Second Law of Thermodynamics, Entropy - 1 - Mechanical Engineering MCQ

Assertion (A): Heat cannot spontaneously pass from a colder system to a hotter system without simultaneously producing other effects in the surroundings.

Reason (R): External work must be put into heat pump so that heat can be transferred from a cold to a hot body.

An inventor says that his new concept of an engine, while working between temperature limits of 27°C and 327°C rejects 45% of heat absorbed from the source. His engine is then equivalent to which one of the following engines?

Assertion (A): Efficiency of a reversible engine operating between temperature limits T₁ and T₂ is maximum.

Reason (R): Efficiency of a reversible engine is greater than that of an irreversible engine.

When a process becomes irreversible due to heat interaction between system and surrounding at the boundary due to finite temperature gradient, then the irreversibility is______

A reversible engine operates between temperatures 900 K & T₂ (T₂ < 900 K), & another reversible engine between T₂ & 400 K (T₂ > 400 K) in series. What is the value of T₂ if work outputs of both the engines are equal?

Two reversible engine operate between thermal reservoirs at 1200 K, T₂K and 300 K such that 1^st engine receives heat from 1200 K reservoir and rejects heat to thermal reservoir at T₂K, while the 2^nd engine receives heat from thermal  reservoir at T₂K and rejects heat to the thermal reservoir at 300 K. The efficiency of both the engines is equal.

What is the value of temperature T₂?

An engine working on Carnot cycle rejects 40% of absorbed heat from the source, while the sink temperature is maintained at 27°C, then what is the source temperature?

A reversible heat engine rejects 50 percent of the heat supplied during a cycle of operation. If this engine is reversed and operates as a heat pump, then what is its coefficient of performance?

One reversible heat engine operates between 1600 K and T₂ K, and another reversible heat engine operates between T₂K and 400 K. If both the engines have the same heat input and output, then the temperature T₂ must be equal to:

Assertion (A): No machine would continuously supply work without expenditure of some other form of energy.

Reason (R): Energy can be neither created nor destroyed, but it can only be transformed from one form into another.

A reversible engine En as shown in the given figure draws 300 kcal from 200 K reservoir and does 50 kcal of work during a cycle. The sum of heat interactions with the other two reservoir is given by:

In a cyclic heat engine operating between a source temperature of 600°C and a sink temperature of 20°C, the least rate of heat rejection per kW net output of the engine is

An ideal gas of mass m and temperature T₁ undergoes a reversible isothermal process from an initial pressure P₁ to final pressure P₂. The heat loss during the process is Q. The entropy change ΔS of the gas is

Nitrogen gas (molecular weight 28) is enclosed in a cylinder by a piston, at the initial condition of 2 bar, 298 K and 1 m³. In a particular process, the gas slowly expands under isothermal condition, until the volume becomes 2m³. Heat exchange occurs with the atmosphere at 298 K during this process.

The entropy change for the Universe during the process in kJ/K is

One kilogram of water at room temperature is brought into contact with a high temperature thermal reservoir. The entropy change of the universe is:

The ratio of root mean square velocity to average velocity of gas molecules at a particular temperature is

Which of the following statement is correct?