arthham

JEE Advanced 2023 · Thermodynamics

One mole of an ideal gas undergoes two different cyclic processes I and II, as shown in the P−VP-V diagrams below. In cycle I, processes aa, bb, cc and dd are isobaric, isothermal, isobaric and isochoric, respectively. In cycle II, processes a′a', b′b', c′c' and d′d' are isothermal, isochoric, isobaric and isochoric, respectively. The total work done during cycle I is WIW_I and that during cycle II is WIIW_{II}. The ratio WI/WIIW_I/W_{II} is ______.

Answer: 22

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Written solution

Step 1: Analyze the processes in Cycle I.

Calculate the work done in each individual process of Cycle I.

Wa=4P0(2V0−V0)=4P0V0W_a = 4P_0(2V_0 - V_0) = 4P_0V_0 Wb=∫2V04V08P0V0V dV=8P0V0ln⁡2W_b = \int_{2V_0}^{4V_0} \frac{8P_0V_0}{V} \, dV = 8P_0V_0 \ln 2 Wc=2P0(V0−4V0)=−6P0V0W_c = 2P_0(V_0 - 4V_0) = -6P_0V_0 Wd=0W_d = 0

Step 2: Calculate the total work done in Cycle I (WIW_I).

Sum the work done in all four processes of Cycle I.

WI=Wa+Wb+Wc+WdW_I = W_a + W_b + W_c + W_d WI=4P0V0+8P0V0ln⁡2−6P0V0W_I = 4P_0V_0 + 8P_0V_0 \ln 2 - 6P_0V_0 WI=(8ln⁡2−2)P0V0W_I = (8\ln 2 - 2)P_0V_0

Step 3: Analyze the processes in Cycle II.

Calculate the work done in each individual process of Cycle II.

Wa′=∫V02V04P0V0V dV=4P0V0ln⁡2W_{a'} = \int_{V_0}^{2V_0} \frac{4P_0V_0}{V} \, dV = 4P_0V_0 \ln 2 Wb′=0W_{b'} = 0 Wc′=P0(V0−2V0)=−P0V0W_{c'} = P_0(V_0 - 2V_0) = -P_0V_0 Wd′=0W_{d'} = 0

Step 4: Calculate the total work done in Cycle II (WIIW_{II}).

Sum the work done in all four processes of Cycle II.

WII=Wa′+Wb′+Wc′+Wd′W_{II} = W_{a'} + W_{b'} + W_{c'} + W_{d'} WII=(4ln⁡2−1)P0V0W_{II} = (4\ln 2 - 1)P_0V_0

Step 5: Find the ratio of the work done in the two cycles.

Divide the total work of Cycle I by the total work of Cycle II.

WIWII=(8ln⁡2−2)P0V0(4ln⁡2−1)P0V0\frac{W_I}{W_{II}} = \frac{(8\ln 2 - 2)P_0V_0}{(4\ln 2 - 1)P_0V_0} WIWII=2(4ln⁡2−1)4ln⁡2−1\frac{W_I}{W_{II}} = \frac{2(4\ln 2 - 1)}{4\ln 2 - 1} WIWII=2\frac{W_I}{W_{II}} = 2

Answer: 2

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