Monday 9 December 2013

Heat ...problems...10 dec 13

1-An ideal gas is filled in a cylinder fitted with a movable piston at one end. Pressure in the cylinder is P. Now the piston is suddenly pushed to compress the gas to one fourth of it's initial volume and held in same position for long time so that the gas attains a thermal equilibrium with surrounding . If the adiabatic constant for the gas is 1.5 then what is the final pressure ? Show the whole process once in p-V graph and then in T - V graph.

Answer : 4P; fig-a and fig -b



2-An ideal gas is filled in a cylinder fitted with a movable piston at one end. Pressure in the cylinder is P and the volume is V . Now the piston is suddenly pushed to compress the gas to one fourth of it's initial volume and held in same position for long time so that the gas attains a thermal equilibrium with surrounding . Now the gas is allowed to expand isothermally to initial volume V. If the adiabatic constant for the gas is 1.5 ,what is net amount of heat absorbed by the gas ?

Hint :
When the gas is compressed adaibatically, no heat is exchanged .During constant volume cooling heat is released. This amount of the heat released can be obtained using the concept of heat capacity at constant volume i.e. Q = n Cv (Tf-Ti). During isothermal expansion,heat is absorbed according to the relation PV ln (Vf/Vi).






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