AMJ21003 Thermodynamics: Chapter 6

Which statement best describes the Second Law of Thermodynamics?

• Energy cannot be created or destroyed, only converted.

• Heat always flows from a cooler body to a hotter body spontaneously.

• Heat cannot be completely converted into work in a cyclic process.

• The total energy of an isolated system remains constant.

How does the Second Law of Thermodynamics differ from the First Law?

• The First Law defines energy conservation, while the Second Law introduces entropy.

• The Second Law states that energy is always conserved.

• The First Law limits the direction of heat transfer.

• The First Law deals with entropy increase in a closed system.

A heat engine receives 600 kJ of heat from a high-temperature source and rejects 250 kJ to a low-temperature sink. What is the net work output?

• 250 kJ

• 350 kJ

• 600 kJ

• 850 kJ

A steam power plant receives 500 kJ of heat and produces 200 kJ of useful work. What is its thermal efficiency?

• 25%

• 35%

• 40%

• 50%

A refrigerator removes 1200 kJ of heat from the inside while consuming 400 kJ of work. What is its Coefficient of Performance (COP)?

• 2.0

• 3.0

• 4.0

• 5.0

A heat pump extracts 800 kJ from a cold environment while consuming 200 kJ of work. How much heat is delivered to the heated space?

• 600 kJ

• 800 kJ

• 1000 kJ

• 1200 kJ

Which of the following is not an example of a reversible process?

• Frictionless piston movement

• Heat transfer through an infinitesimal temperature difference

• Mixing of two gases spontaneously

• Expansion of gas in a well-insulated cylinder

A Carnot heat engine operates between heat reservoirs at 327°C and 27°C. What is its thermal efficiency?

• 25%

• 35%

• 50%

• 66%

Malaysia is increasingly investing in geothermal energy as a renewable power source. A geothermal power plant extracts heat from underground reservoirs at 727°C and releases waste heat to the surrounding environment at 27°C.
Given that the Carnot cycle represents the theoretical maximum efficiency of a heat engine operating between two temperature reservoirs, determine the maximum possible efficiency of this geothermal power plant.

• 30%

• 50%

• 70%

• 80%

Malaysia still relies heavily on coal-fired power plants to meet its electricity demands. A newly constructed coal power plant in Johor is expected to supply 500 MW of net electricity to the national grid. However, due to energy losses, the plant operates at an overall efficiency of 38%.

Based on this information, determine the total thermal energy input required per second to operate this power plant.

• 850 MW

• 900 MW

• 1316 MW

• 1700 MW