Practise 29 real Federal Board questions on Thermodynamics from 2023 to 2026. See the answer and explanation as soon as you answer.
Thermodynamics is one of the 14 main chapters in our Federal Board FSC Physics question bank (11th and 12th class), and about 6% of its real questions come from it. Tayyari Karo has 29 real questions on this chapter from 2023 to 2026; 7 are multiple choice and marked instantly, and the rest are short and long questions with a model answer. By difficulty: 20 medium, 9 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
If the temperature of the heat source is doubled than before, efficiency increases by:
Answer: A. 1.5 times
For a typical Carnot engine (e.g. Tₕ=600K, T_c=300K), η=50%; doubling Tₕ to 1200K gives η=1−300/1200=75% — an increase by a factor of 1.5.
In an adiabatic process, which quantity remains constant?
Answer: D. Mass
In an adiabatic process (Q=0) with a closed system, only the mass of the gas remains constant — internal energy, temperature and volume all generally change.
The work done by a gas at constant pressure is given by:
Answer: A. P·ΔV
At constant pressure, work done by a gas W = PΔV.
The first law of thermodynamics is expressed as:
Answer: C. Q = ΔU + W
The first law states heat supplied Q equals the increase in internal energy plus work done: Q = ΔU + W.
For an ideal gas, the internal energy is directly proportional to:
Answer: B. Temperature
For an ideal gas, internal energy arises purely from molecular kinetic energy: U = (3/2)nRT, so U ∝ T.
Which of the following has higher efficiency? An engine working between the temperatures:
Answer: C. 40K and 20K
Carnot efficiency = 1 − T_cold/T_hot. For 40K/20K, efficiency = 1 − 20/40 = 0.5 (50%), the highest among the given pairs.
In thermodynamics briefly describe: (a) Reversible process, (b) Irreversible process, (c) Cyclic process.
(a) Reversible process: an idealized process that occurs infinitely slowly through a continuous series of equilibrium states, such that both the system and surroundings can be restored to their exact original states with no net change anywhere (no real process is perfectly reversible).
(b) Irreversible process: a process that cannot be reversed to restore both the system and surroundings to their original states without some permanent change — all real, naturally occurring processes are irreversible (e.g. due to friction, finite temperature differences). …
The full model answer is in the app.
State three statements of the second law of thermodynamics (one in terms of entropy).
1. Kelvin–Planck statement: No heat engine can convert all the heat absorbed from a hot reservoir completely into work; some heat must be rejected to a cold reservoir.
2. Clausius statement: Heat cannot flow, by itself, from a colder body to a hotter body without external work being done.
3. Entropy statement: The total entropy of an isolated system can never decrease; it either increases (for real, irreversible processes) or stays constant (for an idealized reversible process).
| Session | Questions |
|---|---|
| 2026 Annual | 9 |
| 2025 1st Annual | 5 |
| 2025 2nd Annual | 5 |
| 2024 Annual | 5 |
| 2023 Annual | 5 |
29 real Federal Board (FBISE) Physics questions on Thermodynamics from 2023 to 2026, for 11th and 12th class. Each one shows the session it came from.
No. We could not find an official FBISE marking scheme for these papers, so the answers and explanations are written by Tayyari Karo for practice. Check anything important with your teacher or textbook.
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