Question 51:
moderateWater rises to height ‘$h$’ in capillary tube. If the length of capillary tube above the surface of water is made less than ‘$h$’, then:
(2015 Re)
When a capillary tube is of insufficient length, the liquid rises to the top and changes its meniscus radius to maintain equilibrium ($hR = \text{constant}$). It does not overflow.
Question 52:
moderateThe wettability of a surface by a liquid depends primarily on:
(2013)
Wettability directly depends on the angle of contact. If the angle is acute, the liquid wets the solid; if it is obtuse, it does not wet the solid.
Question 53:
moderateThe velocity of a small ball of mass $M$ and density $d$, when dropped in a container filled with glycerine becomes constant after some time. If the density of glycerine is $\frac{d}{2}$, then the viscous force acting on the ball will be:
(2021)
At constant terminal velocity, net force is zero. Viscous force $F_v = \text{Weight} - \text{Buoyant force}$. $$F_v = Vdg - V\left(\frac{d}{2}\right)g = \frac{Vdg}{2} = \frac{Mg}{2}$$.