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  3. Physics
  4. The narrow tube with one of its ends sealed as shown in the figure, is in a vertical plane. In the 3 L long horizontal part of the tube, a mercury column of length L blocks some oxygen gas of length L. The outside air pressure of P0 is equal to the pressure of a mercury column of height L. Increasing the temperature of the surrounding, the volume of the blocked gas doubles while the gas absorbs Q=7 J of heat from its surroundings. How much work (in joule) is done by the expanding gas?

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Q. The narrow tube with one of its ends sealed as shown in the figure, is in a vertical plane. In the $3 L$ long horizontal part of the tube, a mercury column of length $L$ blocks some oxygen gas of length $L$. The outside air pressure of $P_{0}$ is equal to the pressure of a mercury column of height $L$. Increasing the temperature of the surrounding, the volume of the blocked gas doubles while the gas absorbs $Q=7 J$ of heat from its surroundings. How much work (in joule) is done by the expanding gas?Physics Question Image

Thermodynamics

Solution:

$Q=7 \,J ; \Delta Q=\Delta U+W$
$\Rightarrow 7=n C_{v} \Delta T+P d V=n \frac{5}{2} R \Delta T+n R \Delta T$
$7=\frac{7}{2}(n R \Delta T) $
$\Rightarrow n R \Delta T=2\, J$