Two identical rigid glass bulbs of equal volume are connected by a narrow valve that…
PHYSICS · Multi-part · A Level · Physics · Further mechanics and thermal physics · Further mechanics and thermal physics
Problem
Two identical rigid glass bulbs of equal volume are connected by a narrow valve that can be opened or closed. Both bulbs initially contain the same ideal gas at pressure P0 and temperature T0. While the valve is closed, one bulb is slowly compressed with an external movable piston until the gas in that bulb reaches a pressure of 1.5P0; the other bulb is left unchanged. The piston is then locked in place so that the volumes of the two bulbs remain fixed. The valve is now opened and the system is allowed to reach a new equilibrium. Throughout the entire process the apparatus is thermally insulated so that no heat is exchanged with the surroundings.
(a) After equilibrium has been reached with the valve open, state the relationship between the pressures in the two bulbs.
(b) Using molecular-level reasoning, explain why the pressures attain the relationship identified in part (a) even though the volumes of the two bulbs remain fixed.
(c) Describe qualitatively how the number of gas molecules in each bulb changes during the equilibration process and explain the cause of any transfer of molecules.
(d) Once equilibrium is achieved, there is no macroscopic gas flow through the valve even though molecules cross the opening in both directions. Explain, in terms of Newton’s laws applied to individual molecular collisions, why this absence of net flow is consistent with the pressure you described in part (a).