A frictionless heat engine can be 100% if:
Correct answer: B. The temperature of the sink is 0 K.
- A. The temperature of the sink is 0°C.
- B. The temperature of the sink is 0 K.
- C. The temperature of the source is 0.
- D. The temperature of the sink is equal to the temperature of the source.
Explanation
Heat engines can't achieve 100% thermal efficiency according to the Second law of thermodynamics. This is impossible because some waste heat is always produced in a heat engine, shown in Figure 1 by the term. Heat engines often operate at around 30% to 50% efficiency, due to practical limitations. Heat engines can't achieve 100% thermal efficiency. η=1 According to the Second law of thermodynamics, this is impossible because some waste heat is always produced in a heat engine, shown in Figure 1 by the QL term. Although complete efficiency in a heat engine is impossible, there are many ways to increase a system's overall efficiency.
This question appeared on the HEC Phase I 2017 paper, which you can sit online with every answer explained.
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About Thermal Equilibrium and Heat
Thermal equilibrium means that bodies in contact have the same temperature and no net heat flows between them. The topic distinguishes heat from temperature, uses the zeroth law of thermodynamics, and covers heat transfer, specific heat capacity, thermal expansion and the conditions for reaching equilibrium.
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