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Thermodynamics

24 free MDCAT Physics MCQs on Thermodynamics (PM&DC syllabus), each with the answer, an explanation and the textbook line it comes from. Tap to check, no sign-up.

MDCAT (Pakistan)PhysicsPre-medical (Grade 12)24 questions

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  1. Question 1

    Energy that flows from a hotter body to a colder one, until their temperatures become equal, is called:

    Show answer and explanation

    Answer: A) Heat

    Heat is energy in transit due to a temperature difference. Source: PHYSICS 11 KPK (taleem360.com), p. 347.

  2. Question 2

    A thermodynamic process carried out with the volume of the system held constant is:

    Show answer and explanation

    Answer: C) Isochoric

    Its P-V graph (isochor) is parallel to the pressure axis. Source: PHYSICS 11 KPK (taleem360.com), p. 355.

  3. Question 3

    A thermodynamic process carried out with the pressure held constant is:

    Show answer and explanation

    Answer: D) Isobaric

    Its graph (isobar) is parallel to the volume axis. Source: PHYSICS 11 KPK (taleem360.com), p. 356.

  4. Question 4

    A process during which no heat enters or leaves the system is called:

    Show answer and explanation

    Answer: A) Adiabatic

    Delta Q = 0; achieved by insulation or by doing the process quickly. Source: PHYSICS 11 KPK (taleem360.com), p. 358.

  5. Question 5

    The currently accepted value of the mechanical equivalent of heat J is:

    Show answer and explanation

    Answer: A) 4.18 J/cal

    In SI units (work and heat both in joules) it equals one. Source: PHYSICS 11 KPK (taleem360.com), p. 349.

  6. Question 6

    Count Rumford observed heat given off while boring gun metal, showing heat is a form of energy, in:

    Show answer and explanation

    Answer: C) 1798

    Joule measured the mechanical equivalent in 1845. Source: PHYSICS 11 KPK (taleem360.com), p. 348.

  7. Question 7

    Rudolf Clausius introduced the concept of entropy into thermodynamics in:

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    Answer: A) 1856

    It gave a quantitative basis for the second law. Source: PHYSICS 11 KPK (taleem360.com), p. 374.

  8. Question 8

    The first successful petrol engine was invented by Nikolaus Otto in:

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    Answer: B) 1876

    Rudolph Diesel's engine followed in 1892. Source: PHYSICS 11 KPK (taleem360.com), p. 371.

  9. Question 9

    The triple point of water is:

    Show answer and explanation

    Answer: D) 273.16 K

    Ice, water and vapour co-exist at this temperature. Source: PHYSICS 11 KPK (taleem360.com), p. 378.

  10. Question 10

    A heat engine is supplied 65.0 kcal of heat and exhausts 40.0 kcal (1 kcal = 4184 J). The work done is about:

    Show answer and explanation

    Answer: A) 105 kJ

    W = 4184 x (65.0 - 40.0) = 104,600 J = 105 kJ. Source: PHYSICS 11 KPK (taleem360.com), p. 349.

  11. Question 11

    A system receives 25200 J of heat and performs 6000 J of work on its surroundings. Its internal energy changes by:

    Show answer and explanation

    Answer: C) 19200 J

    Delta U = 25200 - 6000 = 19200 J. Source: PHYSICS 11 KPK (taleem360.com), p. 380.

  12. Question 12

    The internal energy of a gas decreases by 200 J while the gas does 50 J of work. The heat transferred is:

    Show answer and explanation

    Answer: D) 150 J given out

    Q = Delta U + W = -200 + 50 = -150 J; the negative sign means heat leaves the gas. Source: 11 Physics Book FBISE, p. 140.

  13. Question 13

    The efficiency of a Carnot engine working between the steam point and the ice point is about:

    Show answer and explanation

    Answer: B) 26.8%

    1 - 273/373 = 0.268. Source: PHYSICS 11 KPK (taleem360.com), p. 380.

  14. Question 14

    A Carnot engine of maximum efficiency 55% has its source at 600 K. The temperature of its sink is:

    Show answer and explanation

    Answer: C) 324 K

    T2 = T1 (1 - efficiency) = 600 x 0.45 = 324 K. Source: PHYSICS 11 KPK (taleem360.com), p. 372.

  15. Question 15

    The work done by a gas can be found from the area under its:

    Show answer and explanation

    Answer: B) P-V graph

    Area = P x Delta V. Source: 11 Physics Book FBISE, p. 132.

  16. Question 16

    When a gas expands, the work done by the gas on its surroundings is taken as:

    Show answer and explanation

    Answer: C) Positive

    When the gas is compressed, work is done on it (negative). Source: 11 Physics Book FBISE, p. 133.

  17. Question 17

    In an isochoric process, all the heat supplied to a gas goes into:

    Show answer and explanation

    Answer: D) Its internal energy

    Delta V = 0, so W = 0 and Delta Q = Delta U. Source: PHYSICS 11 KPK (taleem360.com), p. 356.

  18. Question 18

    During an isothermal expansion of an ideal gas, the heat supplied is:

    Show answer and explanation

    Answer: A) Equal to the work done

    Delta U = 0 at constant temperature, so Delta Q = Delta W. Source: PHYSICS 11 KPK (taleem360.com), p. 358.

  19. Question 19

    When a gas is allowed to expand suddenly (adiabatically), its temperature will:

    Show answer and explanation

    Answer: B) Decrease

    The work is done at the cost of internal energy. Source: PHYSICS 11 KPK (taleem360.com), p. 359.

  20. Question 20

    When a gas is compressed adiabatically, its temperature and internal energy:

    Show answer and explanation

    Answer: C) Increase

    Work done on the gas raises its internal energy, e.g. a tyre pump warms up. Source: 11 Physics Book FBISE, p. 137.

  21. Question 21

    In an adiabatic expansion, the work done by the gas is obtained from its:

    Show answer and explanation

    Answer: D) Internal energy

    Delta Q = 0, so Delta W = -Delta U. Source: PHYSICS 11 KPK (taleem360.com), p. 359.

  22. Question 22

    The change in internal energy of a system taken from one state to another depends on:

    Show answer and explanation

    Answer: B) Only initial and final states

    Internal energy is a state variable. Source: PHYSICS 11 KPK (taleem360.com), p. 354.

  23. Question 23

    The internal energy of an ideal gas depends only on its:

    Show answer and explanation

    Answer: C) Temperature

    There are no intermolecular forces in an ideal gas. Source: PHYSICS 11 KPK (taleem360.com), p. 357.

  24. Question 24

    The efficiency of a Carnot engine depends on the:

    Show answer and explanation

    Answer: A) Reservoir temperatures

    Efficiency = 1 - T2/T1, independent of the working substance. Source: PHYSICS 11 KPK (taleem360.com), p. 371.

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