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				   We know that dW = F.dx

In an isothermal system, pressure is being applied by the gas which moves the piston upwards.

So dW = Pgas.A.dx = Pgas.dV

But in all books it is mentioned that dW=Pext.dV.

Can you please clarify on this?

6 years ago


Answers : (2)


Here the pressure is external to the system and opposing the expansion, dw=Pext*dV




6 years ago

The work is done against external pressure, but the work is being done BY the gas, so we consider the force that the gas exerts.
Work done by a body depends upon the force exerted BY the body, not on the force against which the work is being done, right??
For example, let us consider two men A and B pushing a block in opp. directions with force F and G by A and B resp. Then work done by A = F.x

Then why are we considering the opposing factor in case of gases?
6 years ago

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