$A$ capillary tube is dipped in water and it is $20 \, cm$ outside water. The water rises up to $8 \, cm$. If the entire arrangement is put in a freely falling elevator,the length of the water column in the capillary tube will be ........ $cm$.

The sap in a tree rises in a system of capillaries of radius $2.5 \times 10^{-5} \, m$. The surface tension of the sap is $7.28 \times 10^{-2} \, N \, m^{-1}$ and the angle of contact is $0^{\circ}$. The maximum height to which the sap can rise in a tree through capillarity action is ...... $m$ (take $\rho_{sap} = 10^3 \, kg \, m^{-3}$ and $g = 9.8 \, m \, s^{-2}$).

Give reason: The lighting of a lamp is due to the wick of the lamp.

Two vertical parallel plates are partially submerged in water. The distance between the plates is equal to $d$. Water rises due to surface tension $T$,the width of the plates is $l$,and the contact angle of water with glass is $0^o$. Find the force of attraction between the plates.

$A$ capillary tube of radius $r$ is immersed in water and water rises in it to a height $h$. The mass of the water in the capillary tube is $m$. Another capillary of radius $2r$ is immersed in water. The mass of water that will rise in this tube is

$A$ capillary tube of radius $R$ is immersed in water and water rises in it to a height $H$. The mass of water in the capillary tube is $M$. If the radius of the tube is halved,the mass of water that will rise in the capillary tube will now be