Solid and Fluids - NEET Physics Questions
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Solid and Fluids

Question 51: moderate

Water 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)

1. Water does not rise at all.
2. Water rises up to the tip of capillary tube and then starts overflowing like a fountain.
3. Water rises up to the top of capillary tube and stays there without overflowing.
4. Water rises up to a point a little below the top and stays there.
View Answer

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: moderate

The wettability of a surface by a liquid depends primarily on:

(2013)

1. Angle of contact between the surface and the liquid
2. Viscosity
3. Surface tension
4. Density
View Answer

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: moderate

The 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)

1. $Mg$
2. $\frac{3}{2}Mg$
3. $2Mg$
4. $\frac{Mg}{2}$
View Answer

At constant terminal velocity, net force is zero. Viscous force $F_v = \text{Weight} - \text{Buoyant force}$. $$F_v = Vdg - V\left(\frac{d}{2}\right)g = \frac{Vdg}{2} = \frac{Mg}{2}$$.