JEE Advanced 2018 · Paper 1 · Physics Q6

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PhysicsMultiple correct+4 / -2Question 6 of 54

One mole of a monatomic ideal gas undergoes a cyclic process as shown in the figure (where $V$ is the volume and $T$ is the temperature). Which of the statements below is (are) true?

T-V diagram of a cycle: I is a curve rising steeply from low T to high T as V decreases slightly; II is horizontal at the high temperature with V increasing; III is a curve falling from high T to low T as V increases; IV is horizontal at the low temperature with V decreasing.

Process I is an isochoric process

In process II, gas absorbs heat

In process IV, gas releases heat

Processes I and III are not isobaric

Answer and worked solution

Official answer: B, C, D

In a $T$ - $V$ diagram an isobar is a straight line through the origin ( $V\propto T$ ) and an isotherm is horizontal.

(A) In process I the volume changes (it decreases slightly) while $T$ rises. Not isochoric. False.
(B) Process II is isothermal expansion: $\Delta U=0$ and $W>0$ , so $Q=W>0$ . The gas absorbs heat. True.
(C) Process IV is isothermal compression: $W<0$ , so $Q<0$ . The gas releases heat. True.
(D) In I, $T$ rises while $V$ falls; in III, $T$ falls while $V$ rises. Neither has $V\propto T$ , so neither is isobaric. True.

(B), (C), (D)

Topics:Thermodynamic processes First law and internal energy

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JEE Advanced 2018 · Paper 1, Physics question 6