Suppose there are n molecules of gas in a cylindrical container fitted with a piston. The force that was needed to keep the piston at a certain height depends upon the no. of molecules colliding with the piston(this is nothing but the pressure). Suppose if we increase the area of the piston we get no. of molecules colliding with the piston also increases proportional to the area. So, the pressure should increase. But if we take boyle's law at constant temperature with increasing area pressure should decrease!!contradictory!! Can someone tell me where I went wrong?
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The force that was needed to keep the piston at a certain height depends upon the no. of molecules colliding with the piston(this is nothing but the pressure).
Actually, this is nothing but the pressure times the area. The pressure depends on the number of molecules colliding with the piston per unit area (and also how hard they hit). The force on the piston depends not just on the pressure, but also on the area. So, if you increase the area of the piston (which basically means changing to different cylindrical container with the same volume) you can increase the force on the piston without changing the pressure.
Boyle's law says nothing about area. Changing the area of the piston without changing the volume doesn't affect the pressure.
