KVPY SX SB Exam 2018 Question Paper

Question : 96 of 120

Marks: +1, -0

Graphs below show the entropy vs energy (U) of two system I and Ii at constant volume. The initial energies of the systems are indicated by

U_{I,i}

and U

_{II,i}

, respectively. Graphs are drawn to the same scale. The system are then brought into thermal contact with each other. Assume that at all times the combined energy of the two systems remains constant. Choose the most appropriate option indicating the energies of the two systems and the total entropy after they achieve the equilibrium.

U $_\I$ increases and U $_\II$ decreases and the total entropy remains the same
U $_\I$ decreases and U $_\II$ increases and the total entropy remains the same
U $_\I$ increases and U $_\II$ decreases and the total entropy increases
U $_\I$ decreases and U $_\II$ increases and the total entropy increases

Validate

Solution:

∆S_1={∆Q_1}/T_1

→ negative

∆S_1={∆Q_2}/T_2

→ positive

{∆Q_1}={∆Q_2}

T_1 > T_2

∆S_1 < ∆S_2

∆S= ∆S_1 + ∆S_2 > 0

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