JEE Main 2021 · 16 March · morning · Single correct · +4 / −1

In thermodynamics, heat and work are :

  1. (a) Path functions
  2. (b) Point functions
  3. (c) Extensive thermodynamics state variables
  4. (d) Intensive thermodynamic state variables
Answer and solution

Answer (a) Path functions

Solution

Physics sir · 4 steps

Ask one question: does the amount depend on the route you took? For heat and work, it does.

  1. Point function. A point function depends only on the state of the system, like P, V, T or internal energy U. Going from state A to state B, its change is the same whatever route you take.
  2. Work depends on path. Work is the area under the curve on a P-V diagram, W = ∫ P dV. Two different curves joining the same two states enclose different areas, so they give different work.

    Δ U = Q - W

  3. Heat follows. Δ U is fixed by the end states, but W changes with the path. So Q = Δ U + W must change with the path too.
  4. So. Heat and work are energy in transit during a process. A system does not "contain" them, so they are path functions, option (a).

The idea to keep. State variables (P, V, T, U) describe where the system is. Heat and work describe how it got there, so they always depend on the path.

Answer from the NTA final answer key. Solution by PrepWiser.

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Asked about 150 times in JEE Main since 2020. This question is from 2021.