A gas is contained in a metallic cylinder fitted with a piston. The piston is suddenly moved in to compress the gas and is maintained at this position. As the time passes the pressure of the gas in the cylinder-
a)Increases
b)Decreases
c)remains constant
d)increases or decreases depending on the nature of the gas
My attempt-
1)The cylinder is metallic, so it is not an isolated system i.e. temperature remains constant. (heat is exchanged with the surroundings through conduction,convection,radiation)
As the volume is decreased, pressure must increase in accordance with Boyle's Law.
Unfortunately, the correct answer is b.
2)The gas is compressed suddenly, so we can think it to be an adiabatic process. In compression, internal energy increases and temperature rises, volume is constant, so pressure again has to increase.
I dont understand how the answer is b!!
1I haven't yet done much thermodynamics....but if option B is correct then it seems that the container will have a tendency to PULL the piston inside......
As for your second approach, I would rather say that it is not adiabatic as the question says "As Time Passes "......in that way pressiure should decrease......
(I am confused!)
1no its (b)..read the question again....after compression of the piston the pressure no doubt changes(cant say inc or dec).. but the piston is maintained at this position which implies the volumes of the gas has constant value...so now this new pressure(that changed from first act) decreases...
1@Euclid-
I did not understand you completely. Volume of the gas has a constant value after the piston is maitained at that position. How can we conclude from this that pressure will decrease?