A gas is enclosed in a cylindrical vessel fitted with a frictionless piston. The gas is slowly heated for some time. During the process, 10 J of heat is supplied, and the piston is found to move out 10 cm. Find the increase in the internal energy of the gas. The area of cross section of the cylinder = 4 cm2 and the atmospheric pressure = 100 kPa.
Given
Heat supplied to system ΔQ = 10J
Atmospheric pressure P= 100kPa =100×103Pa
Displacement of the piston d=10cm=0.1m
Area of cross section of cylinder A=4cm2 =410-4m2
Gas will expand when is heat to the system. Therefore, the volume of gas expanded ΔV
ΔV=area ×displacement
=A ×d
ΔV=4×0.1×10-4=40×10-6m3
We know that work done by the gas is given as
ΔW=PΔV
=100×103×40×10-6
ΔW =4J
From first law of thermodynamics, we know that,
ΔQ=ΔU+ΔW
Where ΔQ=heat supplied to the system
ΔU=change in internal energy
ΔW=work done by the system
ΔU=ΔQ-ΔW = 10-4 =6J
Thus, the increase in internal energy is 6J.