Surface Tension

Q.

Why does water form a spherical shape when we used to drop water up or throw water around?

Q.

The apparatus used for the determination of surface tension of a liquid is

1. Thermometer

2. Lactometer

3. Hygrometer

4. Stalagmometer

Q.

Water is filled up to a height h in a beaker of radius R. The density of water is $\rho$, the surface tension of water is T and the atmospheric pressure is $P_0$. Consider a vertical section ABCD of the water column through a diameter of the beaker. The force on water on one side of the section by water on the other side of this section has magnitude:

1. $2P_{0}Rh+\pi R^2\rho gh-2RT$

2. $2P_{0}Rh+R\rho g{h}^2-2RT$

3. $P_0\pi R^2+R\rho g{h}^2-2RT$

4. $P_0\pi R^2+R\rho g{h}^2+2RT$

Q.

Which has more surface tension oil or water?

Q.

Which graph represents the variation of surface tension with temperature over small temperature ranges for water

1. 

2. 

3. 

4. 

Q.

Which of the following contribute to the reason behind the origin of surface tension?

1. only adhesive forces

2. neither cohesive forces nor adhesive forces

3. both cohesive forces and adhesive forces

4. only cohesive forces

Q.

A toothpaste contains soap, which reduces the surface tension and helps it spread freely in mouth.

1. True

2. False

Q.

A light wire AB of length 10 cm can slide on a vertical frame as shown in figure. There is a film of soap solution trapped between the frame and the wire. Find the load W that should be suspended from the wire to keep it in equilibrium. Neglect friction. Surface tension of soap solution = 25 dyne cm^-1. Take g = 10 m s^-2

1. 0.5 kg

2. 50 gm

3. 5 gm

4. 0.5 gm

Q.

For a liquid the coefficients of apparent and real expansions respectively, are related as :

1. Y_a > Y_r

2. Y_a = Y_r

3. Y_a < Y_r

4. nothing can be said

Q. Water rises in a glass capillary tube due to :

1. Surface tension of water
2. Cohesive force of glass molecules
3. Adhesive force between water molecules and the walls of the glass tube
4. Temperature of water

Q. A vertical U-tube of uniform cross-section contains mercury in both sides of its arms as shown below. Gylcerine column of $10cm$ is introduced into one of its arms. Oil of density $0.8g/cc$ is poured into the other arm until the upper surface of the oil and glycerine are at same horizontal level. [${\rho }_{Hg}=13.6g/cc,{\rho }_{glycerine}=1.3g/cc$] The length of oil column is

1. $10.4cm$
2. $8.2cm$
3. $7.2cm$
4. $9.6cm$

Q.

If the temperature increases, the surface tension of a liquid_______.

1. decreases

2. remains the same

3. increases then decreases

4. increases

Q. Why does an object take same time to go up and come down? Although they travel same distance but the force of attraction should be large when it comes down, so logically it should take comparatively less time to come down than to go up (Neglect air resistance)

Q. effect on surface tension with increase in temperature

Q.

Hair of shaving brush clings together when it is taken out of the water due to

1. the force of attraction between the hair

2. surface tension

3. characteristic property of hair

4. viscosity of water

Q. if we apply two forces of 20n and 12n across two ends of a rod of cross section A , will the stress be 12/A ?

Q. A piece of wood of dimensions $1\text{m}\times 2\text{m}\times 3\text{m}$ has a mass of $360\text{kg}$. What is the density of wood in ${\text{kg m}}^{-3}$? Would the wood float in water? ${\rho }_{water}=1000{\text{kg m}}^{-3}$

1. $600\times {10}^{-3},$ No
2. $600,$ No
3. $60\times {10}^{-3},$ Yes
4. $60,$ Yes

Q. A liquid rises to a height of $50cm$ in a capillary tube of diameter $0.04mm$. If density of liquid is $0.08\times {10}^{3}kg$ $m^{-3}$ angle of contact is ${20}^o$, the surface tension of the liquid is ($\cos {20}^o=0.94)$

1. $4.17\frac{N}{m}$
2. $0.417\frac{N}{m}$
3. $4.17\times {10}^{-2}\frac{N}{m}$
4. $4.25\times {10}^{-3}\frac{N}{m}$

Q. Water is poured in a tank through a cylindrical tube of area of cross section $A$ and ejecting water at a constant speed $4m/s$. The tank contains a hole of area $A/2$ at bottom. Level of water in the tank will not go up beyond $take(g=10m/s)$

1. $4.8m$
2. $5.6m$
3. $3.2m$
4. $1.8m$

Q. A glass capillary tube of internal radius $r=0.25mm$ is immersed in water. The top end of the tube projected by $2cm$ above the surface of the water. At what angle does the liquid meet the tube? Surface tension of water $=0.7N/m$.

1. $\theta ={90}^{\circ }$
2. $\theta ={70}^{\circ }$
3. $\theta ={35}^{\circ }$
4. $\theta ={45}^{\circ }$

Q. A uniform glass U-tube is partically filled with a liquid. Horizontal length of the tube is 1 m. Tube is accelerating horizontally with constant acceleration of 6 m$s^{-2}$ . The difference in the heights of the liquid in the two arms of U-tube is-

1. $\frac{6}{10}$ m
2. $\frac{2}{3}$ m
3. $6$ m
4. $\frac{5}{3}$ m

Q. A container contains two immiscible liquids of density ${\rho }_1$ and ${\rho }_2({\rho }_2>{\rho }_1)$. A capillary of radius $r$ is inserted in the liquid so that its bottom reaches up to denser liquid. Denser liquid rises in capillary and attains height equal to $h$ which is also equal to column length of lighter liquid. Assuming zero contact angle find the surface tension of the heavier liquid.

1. $\frac{r{\rho }_{2}gh}{2}$
2. $2\pi r{\rho }_{2}gh$
3. $\frac{r}{2}({\rho }_2-{\rho }_1)gh$
4. $2\pi r({\rho }_2-{\rho }_1)gh$

Q. Water rises to a height of $10cm$ in a capillary tube and mercury falls to a depth of $3.42cm$ in the same capillary tube. If the density of mercury is $13.6gm/cc$ and the angle of contact is ${135}^o$. Find out the ratio of surface tensions of water and mercury.

1. $1:0.5$
2. $2:1$
3. $1:6.5$
4. $1.5:1$

Q. If two capillary tubes of radii $r_1$ and $r_2$ in the ratio $1:2$ are dipped vertically in water, then the ratio of capillary rises in the respective tubes is

1. $1:4$
2. $4:1$
3. $1:2$
4. $2:1$
5. $1:\sqrt{2}$

Q. Three liquids of densities ${\rho }_1$ , ${\rho }_2$, and ${\rho }_3$
$(With{\rho }_1>{\rho }_2>{\rho }_3)$, having the same value of surface tension T, rise to the same height in three identical capillarise. The angles of contact ${\theta }_1$, ${\theta }_2$, and ${\theta }_3$ obey:-

1. $\frac{\pi }{2}<{\theta }_1<{\theta }_2<{\theta }_3<\pi$
2. $\pi >{\theta }_1>{\theta }_2>{\theta }_3>\frac{\pi }{2}$
3. $\frac{\pi }{2}>{\theta }_1>{\theta }_2>{\theta }_3>0$
4. $0\le {\theta }_1<{\theta }_2<{\theta }_3<\frac{\pi }{2}$

Q. What is the shape when a non - wetting liquid is placed in a capillary tube

1. convex downward
2. concave upward
3. convex upward
4. concave downward

Q. Derive an expression for the height of capillary rise between two parallel plates dipping in a liquid of density $\sigma$ separated by a distance d. The surface tension of the liquid is T.

Q. Rise in capillary tube __________ with addition of detergent in pure water.

1. Decreases
2. None of these
3. Remains same
4. Increases