arthham

JEE Advanced 2013 · Thermodynamics

One mole of a monatomic ideal gas is taken along two cyclic processes E → F → G → E and E → F → H → E as shown in the PV diagram. The processes involved are purely isochoric, isobaric, isothermal or adiabatic. Match the paths in List I with the magnitudes of the work done in List II and select the correct answer using the codes given below the lists. List I: P. G → E; Q. G → H; R. F → H; S. F → G. List II:1.160P0V0ln⁡2;2.36P0V0;3.24P0V0;4.31P0V0.: 1. 160 P0V0 \ln_{2}; 2. 36 P0V0; 3. 24 P0V0; 4. 31 P0V0. Options: (1) P→4, Q→3, R→2, S→1; (2) P→4, Q→3, R→1, S→2; (3) P→3, Q→1, R→2, S→4; (4) P→1, Q→3, R→2, S→4.

Answer: A. P→4, Q→3, R→2, S→1P \to 4,\ Q \to 3,\ R \to 2,\ S \to 1

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Written solution

Step 1: Identify the states and processes from the PVPV diagram.

For 1 mole of a monatomic ideal gas, the adiabatic index is γ=53\gamma = \frac{5}{3}. From the given diagram, the coordinates of the states are:

F=(V0,32P0)F = (V_0, 32P_0) E=(V0,P0)E = (V_0, P_0)

The states GG and HH lie on the isobaric line P=P0P = P_0. The processes are identified as:

  • E→FE \to F: Isochoric
  • G→HG \to H and H→EH \to E: Isobaric
  • F→GF \to G: Isothermal
  • F→HF \to H: Adiabatic

Step 2: Calculate the work done for path S (F→GF \to G).

Since F→GF \to G is an isothermal process, the temperature remains constant:

PFVF=PGVGP_F V_F = P_G V_G (32P0)(V0)=P0VG(32P_0)(V_0) = P_0 V_G VG=32V0V_G = 32V_0

The work done during this isothermal expansion is:

WF→G=PFVFln⁡(VGVF)W_{F \to G} = P_F V_F \ln\left(\frac{V_G}{V_F}\right) WF→G=32P0V0ln⁡(32V0V0)W_{F \to G} = 32P_0 V_0 \ln\left(\frac{32V_0}{V_0}\right) WF→G=32P0V0ln⁡(25)=160P0V0ln⁡2W_{F \to G} = 32P_0 V_0 \ln(2^5) = 160P_0 V_0 \ln 2

Thus, S matches with 1.


Step 3: Calculate the work done for path R (F→HF \to H).

Since F→HF \to H is an adiabatic process:

PFVFγ=PHVHγP_F V_F^{\gamma} = P_H V_H^{\gamma}

Substitute γ=53\gamma = \frac{5}{3}:

(32P0)V05/3=P0VH5/3(32P_0) V_0^{5/3} = P_0 V_H^{5/3} VH=(32)3/5V0=8V0V_H = (32)^{3/5} V_0 = 8V_0

The work done during this adiabatic expansion is:

WF→H=PFVF−PHVHγ−1W_{F \to H} = \frac{P_F V_F - P_H V_H}{\gamma - 1} WF→H=32P0V0−P0(8V0)53−1W_{F \to H} = \frac{32P_0 V_0 - P_0 (8V_0)}{\frac{5}{3} - 1} WF→H=24P0V023=36P0V0W_{F \to H} = \frac{24P_0 V_0}{\frac{2}{3}} = 36P_0 V_0

Thus, R matches with 2.


Step 4: Calculate the magnitude of work done for path Q (G→HG \to H).

Since G→HG \to H is an isobaric process at pressure P0P_0:

WG→H=P0(VH−VG)W_{G \to H} = P_0 (V_H - V_G) WG→H=P0(8V0−32V0)=−24P0V0W_{G \to H} = P_0 (8V_0 - 32V_0) = -24P_0 V_0

The magnitude of the work done is:

∣WG→H∣=24P0V0|W_{G \to H}| = 24P_0 V_0

Thus, Q matches with 3.


Step 5: Calculate the magnitude of work done for path P (G→EG \to E).

Since G→EG \to E is an isobaric process at pressure P0P_0:

WG→E=P0(VE−VG)W_{G \to E} = P_0 (V_E - V_G) WG→E=P0(V0−32V0)=−31P0V0W_{G \to E} = P_0 (V_0 - 32V_0) = -31P_0 V_0

The magnitude of the work done is:

∣WG→E∣=31P0V0|W_{G \to E}| = 31P_0 V_0

Thus, P matches with 4.


Answer: The correct matching is: P →\to 4, Q →\to 3, R →\to 2, S →\to 1

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