Capillary Tube
If a tube of very narrow bore (capillary tube) is dipped in a liquid, it is formed that the liquid in the tube either ascent or descents relative to the surrounding liquid. This phenomenon is called capillarity.
The main cause of capillarity is the difference in pressure on two sides concave or convex surface of liquid.
Consider a capillary tube of radius 'r' dipped in a liquid of surface tension 'T' and density ρ.
cosӨ = r/R {R=radius of meniscus}
R = r/ cosӨ
As we know, P = 2T/R
hρg = 2T/R {as P=hρg}
h = 2T / ρgR
h = 2TcosӨ / ρgR
So the height ascent or descent in the capillary tube will be ----
h = 2TcosӨ / ρgR
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