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Heat and Thermodynamics question

2007 · Shift 0 · Q91
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Heat and Thermodynamics question

2007 · Shift 0 · Q91

JEE MainPhysicsHeat and ThermodynamicsMCQ+4 / −1
When a system is taken from state iii to state fff along the path iaf, it is found that Q=50Q=50Q=50 cal and W=20calW=20calW=20cal. Along the path ibfQ=36cal.WibfQ=36cal.WibfQ=36cal.W along the path ibfibfibf is AIEEE 2007 Physics - Heat and Thermodynamics Question 402 English
  1. A
    14cal14cal14cal
  2. B
    6cal6cal6cal
  3. C
    16cal16cal16cal
  4. D
    66cal66cal66cal
View written solutionFree

Correct answer: B

  1. Use the first law of thermodynamics

    For any process,

    ΔU=Q−W\Delta U = Q - WΔU=Q−W

    where:

    • QQQ = heat supplied to the system
    • WWW = work done by the system
  2. From path i→a→fi \to a \to fi→a→f

    Given: Q=50 cal,W=20 calQ = 50\,\text{cal}, \quad W = 20\,\text{cal}Q=50cal,W=20cal

    So,

    ΔUif=50−20=30 cal\Delta U_{if} = 50 - 20 = 30\,\text{cal}ΔUif​=50−20=30cal
  3. Internal energy change is path independent

    Since the system goes from the same initial state iii to the same final state fff, the change in internal energy must be the same for path i→b→fi \to b \to fi→b→f also.

    Thus,

    ΔUif=30 cal\Delta U_{if} = 30\,\text{cal}ΔUif​=30cal
  4. For path i→b→fi \to b \to fi→b→f

    Given: Q=36 calQ = 36\,\text{cal}Q=36cal

    Using

    ΔU=Q−W\Delta U = Q - WΔU=Q−W

    we get

    30=36−W30 = 36 - W30=36−W

    Therefore,

    W=36−30=6 calW = 36 - 30 = 6\,\text{cal}W=36−30=6cal
  5. Match with options

    W=6 calW = 6\,\text{cal}W=6cal

    So the correct option is B.

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