Question

Question 3) Which one of the following statements concerning the efficiency of a Carnot heat engine is true?

A) The efficiency of an irreversible engine is typically greater than that of a reversible engine operating under the same circumstances.

B) The efficiency is dependent on whether an ideal or non-ideal gas is used.

C) One hundred percent efficiency is possible if the engine can be operated in reverse.

D) The efficiency is not dependent on the temperatures of the hot and cold reservoirs.

E) One hundred percent efficiency would be possible if heat could be rejected into a cold reservoir at zero kelvin.

Answer 1

Let us assess the statements one by one

A) This is false. According to the Carnot's theorem of second law of thermodynamics, No engine is more efficient than a reversible Carnot's engine working between same limits of temperature.

B) This is also false. The Carnot efficiency depends only on the source and sink temperatures and not on the working fluid.

2 is sink and 1 is source.

C) This is false. The engine operated in reverse is called Carnot's refrigerator. Its co-efficient of performance is given by

T₁ >T₂

So, this value can be greater than 1, but in this, energy is provided onto the system. Co-efficient of performance and efficiency are different things.

D) This is false. As stated earlier, the efficiency depends on temperature.

E) This statement is true. When T₂ = 0, , meaning 100% efficiency.

So, statements