BR physics question - liquid section

[anbuitachi]

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Hi I have a question. Here it is

There's a reservoir column w/ a drainage pipe at the base. Attached to pipe are 3 columns and a valve. Liquid is allowed to fill in reservoir as valve is closed. The fluid also rises in columns. All columns are open to atmosphere at the top.

Here are the pictures given..

I'm kind of confused about how the height of the liquid in the columns are affected as the valve is opened. Why exactly does column 3 decrease first then 2 then 1 as shown in fig 2?

Also in a question they said the liquid height drops by the same percentage per unit time in column 1 and 2.. Why is that?

Also another question:
The apparatus was redesigned so 1 2 3 had radius of a smaller bore but not so small that capillary forces dominate. How would height of fluid in each change?
I assume since the radius is smaller the pressure would be able to push it higher... but the answer is height won't change noticeably.. Why is that?


Thanks

 

[BerkReviewTeach]

The point of this question is simple, despite the wording not being so simple. Fluids flow from regions of higher pressure to lower pressure according to a pressure gradient. As the fluid flows through the pipe it passes the base of column 1, the base of column 2, and finally the base of column 3. It's dropping in pressure as it flows, so the pressure pushing the fluid up the columns is respectively less and less, resulting in a low height in each successive column. Pressure is force per unit area, so it doesn't matter how wide the vertical columns are.

The second picture should show that the height of the fluid in column 1 is a little lower than the reservoir column, height of the fluid in column 2 is a little lower than the height of the fluid in column 1, and the height of the fluid in column 3 is a little lower than the height of the fluid in column 2.

 

[joshto]

It's dropping in pressure as it flows

Why/how is this so?

simply because there is less fluid "pushing" on it?

 

[anbuitachi]

I see.. that makes a lot of sense lol...