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Heat and Thermodynamics question

2017 · Shift 1 · Q51
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Heat and Thermodynamics question

2017 · Shift 1 · Q51

JEE AdvancedPhysicsHeat and ThermodynamicsMCQ+3 / −0.75
An ideal gas is undergoing a cyclic thermodynamic process in different ways as shown in the corresponding P−VP-VP−V diagram in column 3 of the table. Consider only the path from state 111 to state 2.W2.W2.W denotes the corresponding work done on the system. The equations and plots in the table have standard notations as used in thermodynamic processes. Here YYY is the ratio of heat capacities at constant pressure and constant volume. The number of moles in the gas is n.n.n. JEE Advanced 2017 Paper 1 Offline Physics - Heat and Thermodynamics Question 53 English Comprehension 1 JEE Advanced 2017 Paper 1 Offline Physics - Heat and Thermodynamics Question 53 English Comprehension 2Which one of the following options is the correct combination?
  1. A
    (IV)(ii)(S)\left( {{\rm I}V} \right)\left( {ii} \right)\left( S \right)(IV)(ii)(S)
  2. B
    (III)(ii)(S)\left( {{\rm I}{\rm I}{\rm I}} \right)\left( {ii} \right)\left( S \right)(III)(ii)(S)
  3. C
    (II)(iv)(P)\left( {{\rm I}{\rm I}} \right)\left( {iv} \right)\left( P \right)(II)(iv)(P)
  4. D
    (II)(iv)(R)\left( {{\rm I}{\rm I}} \right)\left( {iv} \right)\left( R \right)(II)(iv)(R)
View written solutionFree

Correct answer: B

Step-by-Step Solution

Step 1: Analyze Column 1 (Work Done Expressions)

The question defines WWW as the work done on the system. The general formula for work done on the system is W=−∫PdVW = -\int P dVW=−∫PdV.

  • (I) W1→2=1γ−1(P2V2−P1V1)W_{1 \rightarrow 2} = \frac{1}{\gamma-1}(P_2V_2 - P_1V_1)W1→2​=γ−11​(P2​V2​−P1​V1​) For an adiabatic process, the work done by the gas is Wby=∫PdV=P1V1−P2V2γ−1W_{by} = \int P dV = \frac{P_1V_1 - P_2V_2}{\gamma-1}Wby​=∫PdV=γ−1P1​V1​−P2​V2​​. The work done on the gas is Won=−Wby=−P1V1−P2V2γ−1=P2V2−P1V1γ−1W_{on} = -W_{by} = -\frac{P_1V_1 - P_2V_2}{\gamma-1} = \frac{P_2V_2 - P_1V_1}{\gamma-1}Won​=−Wby​=−γ−1P1​V1​−P2​V2​​=γ−1P2​V2​−P1​V1​​. This expression corresponds to an adiabatic process.

  • (II) W1→2=−P2(V2−V1)W_{1 \rightarrow 2} = -P_2(V_2 - V_1)W1→2​=−P2​(V2​−V1​) For an isobaric (constant pressure) process, PPP is constant. Let P=P1=P2P = P_1 = P_2P=P1​=P2​. The work done on the system is Won=−∫V1V2PdV=−P(V2−V1)=−P2(V2−V1)W_{on} = -\int_{V_1}^{V_2} P dV = -P(V_2 - V_1) = -P_2(V_2 - V_1)Won​=−∫V1​V2​​PdV=−P(V2​−V1​)=−P2​(V2​−V1​). This expression corresponds to an isobaric process.

  • (III) W1→2=0W_{1 \rightarrow 2} = 0W1→2​=0 Work is done only when there is a change in volume. If W=0W=0W=0, it implies dV=0dV=0dV=0, which means the volume is constant. This corresponds to an isochoric process.

  • (IV) W1→2=−nRTln⁡(V2V1)W_{1 \rightarrow 2} = -nRT \ln(\frac{V_2}{V_1})W1→2​=−nRTln(V1​V2​​) For an isothermal process, temperature TTT is constant. From the ideal gas law, P=nRTVP = \frac{nRT}{V}P=VnRT​. The work done by the gas is Wby=∫V1V2PdV=∫V1V2nRTVdV=nRTln⁡(V2V1)W_{by} = \int_{V_1}^{V_2} P dV = \int_{V_1}^{V_2} \frac{nRT}{V} dV = nRT \ln(\frac{V_2}{V_1})Wby​=∫V1​V2​​PdV=∫V1​V2​​VnRT​dV=nRTln(V1​V2​​). The work done on the gas is Won=−Wby=−nRTln⁡(V2V1)W_{on} = -W_{by} = -nRT \ln(\frac{V_2}{V_1})Won​=−Wby​=−nRTln(V1​V2​​). This expression corresponds to an isothermal process.

Step 2: Match Column 1 with Column 2 (Process Name)

Based on the analysis in Step 1:

  • (I) matches with (iv) Adiabatic
  • (II) matches with (iii) Isobaric
  • (III) matches with (ii) Isochoric
  • (IV) matches with (i) Isothermal

Step 3: Analyze Column 3 (P-V Diagrams)

We analyze the path from state 1 to state 2 in each diagram:

  • (P): The path is a horizontal line, which means pressure is constant. This is an isobaric process.
  • (Q): The path is a curve. The overall cycle resembles an Otto cycle, where the expansion (1 to 2) and compression strokes are adiabatic. The slope of an adiabatic process (dP/dV=−γP/VdP/dV = -\gamma P/VdP/dV=−γP/V) is steeper than that of an isothermal process (dP/dV=−P/VdP/dV = -P/VdP/dV=−P/V). The curve 1->2 is steep, characteristic of an adiabatic process.
  • (R): The path is a curve, less steep than the one in (Q). This is characteristic of an isothermal process.
  • (S): The path is a vertical line, which means volume is constant. This is an isochoric process.

Step 4: Match Column 2 with Column 3

Based on the analysis in Step 3:

  • (i) Isothermal matches with (R)
  • (ii) Isochoric matches with (S)
  • (iii) Isobaric matches with (P)
  • (iv) Adiabatic matches with (Q)

Step 5: Identify the Correct Combination

We now combine the matches to find the correct triplets and check against the given options.

  • Adiabatic: (I) - (iv) - (Q)
  • Isobaric: (II) - (iii) - (P)
  • Isochoric: (III) - (ii) - (S)
  • Isothermal: (IV) - (i) - (R)

Let's evaluate the given options:

  • A: (IV)(ii)(S)\left( {{\rm I}V} \right)\left( {ii} \right)\left( S \right)(IV)(ii)(S) - Incorrect. (IV) is Isothermal, while (ii) and (S) are Isochoric.
  • B: (III)(ii)(S)\left( {{\rm I}{\rm I}{\rm I}} \right)\left( {ii} \right)\left( S \right)(III)(ii)(S) - Correct. (III) is the work for an isochoric process, (ii) is the name for an isochoric process, and (S) is the P-V diagram for an isochoric process.
  • C: (II)(iv)(P)\left( {{\rm I}{\rm I}} \right)\left( {iv} \right)\left( P \right)(II)(iv)(P) - Incorrect. (II) and (P) are Isobaric, but (iv) is Adiabatic.
  • D: (II)(iv)(R)\left( {{\rm I}{\rm I}} \right)\left( {iv} \right)\left( R \right)(II)(iv)(R) - Incorrect. (II) is Isobaric, (iv) is Adiabatic, and (R) is Isothermal.

Thus, the only correct combination listed is B.

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