Real vs Ideal Engine — Practice Quiz

Question 1

An engine has efficiency 30% between T_h = 500 K and T_c = 300 K. Compared to Carnot:

Accepted Answer

Less than Carnot 40%

Answer

Equal

Answer

Exceeds Carnot (impossible)

Answer

Equal to Carnot

Question 2

An engine claims 60% efficiency between 500 K and 300 K. Verdict:

Accepted Answer

Impossible (exceeds Carnot 40%)

Answer

Possible

Answer

Need more data

Answer

Possible if reversed

Question 3

Why are real engines less efficient than Carnot?

Accepted Answer

Friction, finite speed, irreversibilities

Answer

Magnetic field

Answer

Universe expansion

Answer

All real engines are 100% efficient

Question 4

Combined-cycle power plants achieve ~60% efficiency by:

Accepted Answer

Using gas turbine waste heat to power a steam turbine

Answer

Using nuclear fuel

Answer

Hydrogen

Answer

Magnetic effects

Question 5

Carnot's theorem says:

Accepted Answer

No engine can exceed Carnot η between same reservoirs

Answer

All engines equal η

Answer

Engines are 100% efficient

Answer

Heat flows up