Question

What will happen to the rise of liquid in a capillary tube if its top end is closed?

Answer 1

If the top of the capillary tube is closed, there will be a small rise in capillary tube.

Reason :

As we know that the rise of liquid in capillary tube is due to the surface tension  and it is opposed by the downward force exerted by the compressed air above liquid in the tube.

The liquid will rise  till the two forces reach to a equilibrium state  

Therefore there will be small rise in liquid column if the top of capillary tube is closed.

Answer 2

$\bf\huge\color{red}{ANSWER}$

When a fluid is flowing, the pressure drop is caused mainly due to viscous forces.

The effect of viscous forces acting on a fluid depends on the ratio of the surface area of contact with walls to the volume of flow. If you consider a circular cross section (flow through a cylindrical pipe), the pressure drop is proportional to ΔP∝2∗pi∗rpi∗r2ΔP∝2∗pi∗rpi∗r2

So ΔP∝1rΔP∝1r

Thus a small diameter tube shows higher pressure drop.