The discussion revolves around the relationship between pressures in a fluid system involving mercury and water, specifically addressing the equation P3 - P1 = Pb - Pa. Participants are exploring the implications of this equation in the context of fluid statics and the behavior of communicating vessels.
The discussion is ongoing, with participants offering insights into the conditions under which the pressure relationship holds true. There is recognition that the heights of the water columns play a crucial role in determining the validity of the equation, and some participants are suggesting that additional information about these heights is necessary for a complete understanding.
There is a lack of explicit information regarding the heights of the water columns (h1 and h2), which is central to the discussion. The original poster references the law of communicating vessels, but there is uncertainty about its application in this specific scenario.
The law of communicating vessels is based on P3 and P1 being equal. That is not the case here. You will need to know the height of water above a and b. For example if there was no water above a, Pa=P1. But Pb would not be equal to P3. So Pb-Pa is not equal to P3-P1.Cosmossos said:In the question I have here , it doesn't say anything about h2 and h1. it says that Pb-Pa=P3-P1 thanks to the Communicating_vessels law.But I don't understand why.