12) The gas compresses, and the piston lowers
13) The work done by the gas is
Explanation:
12)
For a gas kept at constant pressure, the work done on the gas is given by:
where
p is the pressure of the gas
is the final volume of the gas
is the initial volume of the gas
We see that when work is done ON the gas, the work done is positive: therefore, this means that the term
must be negative. This implies that
So, the gas has being compressed (by the piston, which lowers down), and its final volume is smaller than the initial volume.
13)
Here we have a gas kept at a constant pressure of
And its initial volume is
The gas is expanded to twice its initial volume, so the final volume is
The work done BY the gas is
Where here we removed the negative sign because this is the work done BY the gas. Substituting, we find
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