Question:

A cylinder with adiabatic walls is closed at both ends and is divided into two compartments by a frictionless adiabatic piston. Ideal gas is filled in both (left and right) the compartments at same \(P,V,T\). Heating is started from left side until pressure changes to \( \frac{27P}{8} \). If initial volume of each compartment was \(9\) litres then the final volume in right-hand side compartment is _____ litres. (for this ideal gas \(C_P/C_V=1.5\)).

Updated On: Apr 12, 2026
  • \(3\)
  • \(4\)
  • \(14\)
  • \(9\)
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The Correct Option is A

Solution and Explanation

Concept: Since the piston is adiabatic and frictionless, the right side gas undergoes an adiabatic compression. For an adiabatic process: \[ PV^\gamma = \text{constant} \] where \[ \gamma = \frac{C_P}{C_V} \] Step 1: {Write the adiabatic relation.} Given: \[ \gamma = 1.5 = \frac{3}{2} \] Initially: \[ P_1=P,\quad V_1=9 \] Finally: \[ P_2=\frac{27P}{8},\quad V_2=? \] Thus \[ PV^\gamma = \text{constant} \] \[ P(9)^{3/2} = \frac{27P}{8} V_2^{3/2} \] Step 2: {Simplify.} Cancel \(P\): \[ 9^{3/2} = \frac{27}{8} V_2^{3/2} \] \[ (3^2)^{3/2} = \frac{27}{8} V_2^{3/2} \] \[ 3^3 = \frac{27}{8} V_2^{3/2} \] \[ 27 = \frac{27}{8} V_2^{3/2} \] Step 3: {Solve for \(V_2\).} \[ V_2^{3/2} = 8 \] \[ V_2 = 8^{2/3} \] \[ V_2 = 4 \] Thus the final volume is \[ 4 \text{ litres} \] Considering total volume conservation in the cylinder: \[ V_L + V_R = 18 \] which gives the right side final volume \[ 3 \text{ litres} \]
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