Physics Thermodynamics 2 ā Questions and Answers
Question 1: Which thermodynamic process occurs at constant pressure?
- Isochoric
- Isobaric (Correct answer)
- Isothermal
- Adiabatic
Correct answer: Isobaric
An isobaric process occurs at constant pressure, so work done equals PĆĪV.
Question 2: A Carnot engine operates between 600 K and 300 K. What is its maximum efficiency?
- 25%
- 33%
- 50% (Correct answer)
- 75%
Correct answer: 50%
Carnot efficiency = 1 ā T_cold/T_hot = 1 ā 300/600 = 0.50 = 50%.
Question 3: When an ideal gas expands adiabatically, its temperature:
- Increases
- Decreases (Correct answer)
- Stays the same
- First increases then decreases
Correct answer: Decreases
In an adiabatic expansion, the gas does work on surroundings with no heat exchange, so internal energy and temperature decrease.
Question 4: The efficiency of a real heat engine compared to a Carnot engine operating between the same temperatures is always:
- Greater
- Equal
- Less (Correct answer)
- Temperature-dependent
Correct answer: Less
Real engines have irreversibilities (friction, heat leaks), making their efficiency always less than the ideal Carnot efficiency.
Question 5: Which quantity is a state function in thermodynamics?
- Work
- Heat
- Enthalpy (Correct answer)
- Both work and heat
Correct answer: Enthalpy
Enthalpy (H = U + PV) is a state function; work and heat are path-dependent process quantities.
Question 6: During a reversible isothermal expansion of an ideal gas, the internal energy:
- Increases
- Decreases
- Remains constant (Correct answer)
- Doubles
Correct answer: Remains constant
For an ideal gas, internal energy depends only on temperature; at constant temperature it remains unchanged.
Question 7: The COP (coefficient of performance) of a refrigerator is defined as:
- W/Q_cold
- Q_cold/W (Correct answer)
- Q_hot/W
- W/Q_hot
Correct answer: Q_cold/W
COP of a refrigerator = heat removed from cold reservoir / work input = Q_cold/W.
Physics Thermodynamics 2
Which thermodynamic process occurs at constant pressure?