MCQ
Consider two containers $A$ and $B$ containing identical gases at the same pressure, volume and temperature. The gas in container $A$ is compressed to half of its original volume isothermally while the gas in container $B$ is compressed to half of its original value adiabatically. The ratio of final pressure of gas in $B$ to that of gas in $A$ is
  • $2^{\gamma-1}$
  • B
    ${\left( {\frac{1}{2}} \right)^{\gamma  - 1}}$
  • C
    ${\left( {\frac{1}{{1 - \gamma }}} \right)^2}$
  • D
    ${\left( {\frac{1}{{\gamma - 1 }}} \right)^2}$

Answer

Correct option: A.
$2^{\gamma-1}$
a
When the compression is isothermal for gas in $A$

$P_{2} V_{2}=P_{1} V_{1}$

$P_{2}=P_{1} \frac{V_{1}}{V_{2}}=P_{1} \frac{V_{1}}{V_{1} / 2}=2 P_{1}$

For gas in $\mathrm{B}$, when compression is adiabatic,

$P_{2}^{\prime} V_{2}^{\prime}=P_{1} V_{1}^{\gamma}$

$P_{2}^{\prime}=P_{1}\left(\frac{V_{1}}{V_{2}^{\prime}}\right)^{\gamma}=P_{1}\left(\frac{V_{1}}{V_{1} / 2}\right)^{\gamma}=2^{\gamma} P_{1}$

$\therefore \frac{P_{2}^{\prime}}{P_{2}}=\frac{2^{\gamma} P_{1}}{2 P_{1}}=2^{\gamma-1}$

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