CHAPTER 4: THERMODYNAMIC CYCLES & SECOND LAW OF THERMODYNAMICS

What does the Second Law of Thermodynamics state about heat transfer?

• A) Heat can spontaneously flow from cold to hot

• B) Heat cannot be converted to work under any circumstances

• C) Heat naturally flows from hot to cold without external influence

• D) The total energy in a system is always decreasing

Which of the following represents the formula for thermal efficiency (ηη) of a heat engine?

• A) η=W_net.out/Q_in

• B) η=Q_out/Q_in

• C) η=Q_in/W_net.out

• D) η=1−(T_L/T_H)

A heat engine receives 200 kJ of heat and rejects 80 kJ. What is its thermal efficiency?

• 60%
• 40%
• 75%
• 50%

Which of the following is true for a Carnot cycle?

• A) It consists of four reversible processes

• B) It has an efficiency of 100%

• C) It can be used to build a perpetual motion machine

• D) It violates the Second Law of Thermodynamics

Which of the following equations correctly defines entropy change (ΔS)?

• A) ΔS=∫dQ/T

• B) ΔS=(Q_in−Q_out)/W

• C) ΔS=W/Q_in

• D) ΔS=T⋅ΔQ

What is the COP (Coefficient of Performance) formula for a refrigerator?

• A) COP_R=Q_H/W

• B) COP_R=Q_L/W

• C) COP_R=W/Q_L

• D)

  COP_R=(Q_H−Q_L)/Q_L

A Carnot engine operates between 600 K and 300 K. What is its thermal efficiency?

• A) 25%

• B) 33%

• C) 50%

• D) 66%

Which statement about entropy is correct?

• A) Entropy always decreases in a closed system

• B) Entropy measures the randomness or disorder of a system

• C) Entropy is conserved in all real processes

• D) Entropy is not related to energy dissipation

Which of the following is the correct efficiency formula for an ideal Carnot cycle?

• A) η=(1−T_L/T_H)

• B) η=W/Q_L

• C) η=Q_H−Q_L

• D) η=T_H−T_L

If a heat pump has a COP of 3 and the input work is 2 kW, how much heat is rejected to the high-temperature reservoir?

• A) 2 kW

• B) 4 kW

• C) 6 kW

• D) 8 kW