If one mole of an ideal gas at P 1 , V 1 is allowed to expand reversibly and isothermally ( A to B ) its…

If one mole of an ideal gas at P1,V1 is allowed to expand reversibly and isothermally (A to B) its pressure is reduced to one-half of the original pressure (see figure). This is followed by a constant volume cooling till its pressure is reduced to one-fourth of the initial value BC. Then it is restored to its initial state by a reversible adiabatic compression (C to A). The net workdone by the gas is equal to:

  1. 0
  2. RTln2
  3. -RT2γ-1
  4. RTln2-12γ-1

Solution

A-B= isothermal process

WAB=P1V1 ln2V1 V1=P1V1ln2

B-C Isochoric process

WBC=0

C-AAdiabatic process

WCA=P1V1-P14×2V11-γ=P1V11-121-γ=P1V121-γ

Wnet=WAB+WBC+WCA  P1V1=RT

=P1V1 ln2+0+P1V121-γ

Wnet=RT ln2-12γ-1

Asked in: JEE Main 2021 (24 Feb Shift 2)

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