Thermodynamics MCQs for MDCAT Practice

Physics section, Thermodynamics chapter. Up to eight free sample questions, each with the correct answer and a worked explanation. The full chapter opens in the app.

1. Question 1
   Substances A and B have the same freezing and boiling points. If solid samples of bothsubstances are heated in the exact same way, substance A boils before substance B.Which of the following would NOT explain this phenomenon?
   • ASubstance B has a higher specific heat.
   • BSubstance B has a higher heat of vaporization.
   • CSubstance B has a higher heat of fusion.
   • DSubstance B has a higher internal energy. (correct answer)
   Correct answer: D

   Substance A boils before B despite same phase transition points, implying differences in energy required for phase changes or temperature increase.
2. Question 2
   The efficiency of a Carnot engine increases when:
   • AThe temperature of the cold reservoir increases
   • BThe temperature of the hot reservoir decreases
   • CThe temperature difference between reservoirs increases (correct answer)
   • DThe pressure of the gas increases
   Correct answer: C

   A Carnot engine's efficiency is maximized by a larger temperature difference between its hot and cold reservoirs.
3. Question 3
   Choose the correct statement?
   • AAdiabat is steeper than isotherm (correct answer)
   • BIsotherm is steeper than isochor
   • CIsobar is steeper than isotherm
   • DAdiabat is steeper than isochor
   Correct answer: A

   Compares the slopes of different thermodynamic processes (isotherm, adiabat, isochor, isobar) on a P-V diagram to understand their relative steepness.
4. Question 4
   The internal energy change of a gas in an isobaric process is given by:
   • AnCvΔT (correct answer)
   • BnCpΔT
   • CPΔV
   • DZero
   Correct answer: A

   Internal energy change ($\Delta U$) depends on heat capacity at constant volume ($C_v$), not constant pressure ($C_p$), even in an isobaric process.
5. Question 5
   In which of the following conditions, does the thermodynamic system DOES NOT perform any work?
   • AAdiabatic condition
   • BIsochoric condition (correct answer)
   • CIsobaric condition
   • DIsothermal condition
   Correct answer: B

   Work done by a thermodynamic system requires a change in volume. Isochoric processes maintain constant volume, thus zero work.
6. Question 6
   A Cu rod and a steel rod maintain a constant difference in their lengths constant = 10 cm at all temperatures. If their coefficients of expansion are 1.6 × 10–5 K–1 and 1.2 × 10–5 K–1, then the length of the Cu rod is:
   • A40 cm
   • B30 cm (correct answer)
   • C32 cm
   • D24 cm
   Correct answer: B

   This question tests understanding of thermal expansion and how differential expansion can maintain a constant length difference between two rods.
7. Question 7
   During adiabatic compression work done is equal to 200 J. What will be the change in internal energy?
   • A-200 J
   • B+200 J (correct answer)
   • C100 J
   • D0 J
   Correct answer: B

   Adiabatic compression: Work done on gas increases its internal energy. This MCQ tests the First Law of Thermodynamics under adiabatic conditions.
8. Question 8
   A gas expands adiabatically, and its temperature decreases. The work done is:
   • AZero
   • BPositive (correct answer)
   • CNegative
   • DEqual to heat supplied
   Correct answer: B

   Adiabatic expansion causes temperature drop and work done by the gas. The First Law of Thermodynamics dictates work sign in such processes.

Read the full Thermodynamics chapter notes: Thermodynamics notes. Or browse every chapter.