Which one of the following equations does not correctly represent the first law of thermodynamics for the given…
Thermodynamics · Class 11 · JEE Main Previous Year Question
Which one of the following equations does not correctly represent the first law of thermodynamics for the given processes involving an ideal gas? (Assume non-expansion work is zero)
- a
Isochoric process:
- b✓
Isochoric process:
- c
Cyclic process:
- d
Adiabatic process:
Isochoric process:
🧠 Which first-law equation doesn't belong to the isochoric process? For an isochoric (constant volume) process: , so . The equation describes a cyclic process, not an isochoric one.
🗺️ Checking each option (a) Isochoric: — Correct. , so . ✓
(b) Isochoric: — Wrong. For isochoric, , so this becomes . That would mean no heat exchange at all — only true if the process is also adiabatic. ✗
(c) Cyclic: — Correct. for cyclic, so . ✓
(d) Adiabatic: — Correct. , and using the convention where = work done by system, . ✓
⚠️ Trap: Option (b) copies the cyclic-process equation and labels it as isochoric. The equations look similar but apply to completely different processes.
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