Surface Tension

Q. It is easy to wash clothes in hot water because its:

1. Surface tension is more
2. Surface tension is less
3. Consumes less soap
4. None of these

Q. A thread is tied loosely to a wire frame as shown in the figure. The frame is taken into a soap solution and taken out. The frame is completely covered with the film. When the portion $A$ is punctured with pin then thread will

1. become concave toward side $A$
2. become concave toward side $B$
3. become straight
4. remain as it is

Q. With an increase in temperature, surface tension of a liquid

1. increases
2. remain constant
3. decreases
4. first decreases then increases

Q. A square wire frame of size $L$ is dipped in a liquid. On taking out, a membrane is formed. If the surface tension of liquid is $T$, then force acting on a frame will be

1. $2TL$
2. $4TL$
3. $8TL$
4. $16TL$

Q.

A container contains two immiscible liquids of density ${\rho }_1$​ and ${\rho }_1({\rho }_2>{\rho }_2)$. 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. $2\pi {\rho }_{2}gh$

2. $\frac{r{\rho }_{2}gh}{2}$

3. $2\pi \left({\rho }_2-{\rho }_1\right)gh$

4. $\frac{r\left({\rho }_2-{\rho }_1\right)gh}{2}$

Q. A thread is tied slightly loose to a wire frame as shown in the figure and the frame is dipped into a soap solution and taken out. The frame is completely covered with the film. When the portion $A$ is punctured with a pin, the thread

1. becomes convex towards $A$.
2. becomes concave towards $A$.
3. remains in the initial position.
4. either (a) or (b) depending on the size of $A$ w.r.t. $B$.

Q. With an increase in temperature, surface tension of a liquid

1. increases
2. remain constant
3. decreases
4. first decreases then increases

Q. A thin liquid film formed between a $U$ - shaped wire and supports a light weight of $1.5\times {10}^{-2}\text{N}$ (see figure). The length of the slider is $30\text{cm}$ and its weight is negligible. The surface tension of the liquid film is

1. $0.0125{\text{Nm}}^{-1}$
2. $0.1{\text{Nm}}^{-1}$
3. $0.05{\text{Nm}}^{-1}$
4. $0.025{\text{Nm}}^{-1}$

Q. At critical temperature, the surface tension of a liquid

1. is zero
2. is infinity
3. is same as that at any other temperature
4. cannot be determined

Q. Identify the incorrect statement regarding surface tension.

1. Due to surface tension, a liquid when spread over any surface tends to form spherical drops.
2. It arises because of intermolecular forces, mainly due to cohesive forces.
3. Surface tension increases, if temperature of liquid is increased keeping other parameters fixed.
4. Surface tension is independent of the surface area of free surface of liquid.

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. Force required to pull a rectangular plate of length $2\text{cm}$ and breadth $3\text{cm}$ from water surface for which surface tension is $75\text{dyne/cm}$ is

1. $200\text{dyne}$
2. $750\text{dyne}$
3. $800\text{dyne}$
4. $600\text{dyne}$

Q. A rectangular film of liquid is extended from $(2\text{cm}\times 8\text{cm})$ to $(4\text{cm}\times 16\text{cm})$. If work done is $5\times {10}^{-4}\text{J}$, value of the surface tension of the liquid is

1. $0.06\text{N/m}$
2. $0.08\text{N/m}$
3. $0.05\text{N/m}$
4. $0.09\text{N/m}$

Q.

A soap bubble of radius r is blown up to form a bubble of radius 2r under isothermal conditions. If $\sigma$ is the surface tension of soap solution, the energy spent in doing so is

1. $3\pi \sigma r^2$

2. $6\pi \sigma r^2$

3. $12\pi \sigma r^2$

4. $24\pi \sigma r^2$

Q. Two separate bubbles (radii 0.002 m and 0.004 m) formed of the same soap solution (surface tension = 0.07 N/m) comes together to form a double bubble. The internal film common to both the bubbles has radius $R$. The value of $R$ (in mm) is (Answer upto two digit after the decimal point)

Q.

Water is kept in a beaker of radius 5.0 cm. Consider a diameter of the beaker on the surface of the water. Find the force by which the surface on one side of the diameter pulls the surface on the other side. Surface tension of water = 0.075 N m^-1.

1. 0.75 N

2. 7.5 × 10^-4 N

3. 7.5 × 10^-3 N

4. 7.5 × 10^-2 N

Q. A container of width $2a$ is filled with a liquid. A thin wire of mass per unit length $\mu$ is gently placed along the middle of the surface as shown in the figure. As a result, the liquid surface is depressed by a distance $y$. The surface tension of the liquid is $\sigma$. Then choose the correct option(s).
[Assume angle of contact between the wire and liquid is acute]

1. $\sigma =\frac{\mu g}{2\cos \theta }$
2. $\sigma =\frac{\mu g}{2\sin \theta }$
3. If $y<<a$, then $\sigma =\frac{\mu ga}{2y}$
4. If $y<<a$, then $\sigma =\frac{\mu ga}{y}$

Q. A $10\text{cm}$ long wire is placed horizontal on the surface of water and is gently pulled up with a force of $2\times {10}^{-2}\text{N}$ to keep the wire in equilibrium. The surface tension (in ${\text{Nm}}^{-1}$) of water is

1. $0.1$
2. $0.2$
3. $0.001$
4. $0.002$

Q. Angle of contact of water on an oily surface is :

1. Acute
2. Obtuse
3. ${90}^{\circ }$
4. $0^{\circ }$

Q. If the length of the free surface of the liquid is doubled, what happens to the surface tension acting on it?

1. It gets doubled.
2. It gets quadrupled.
3. It remains the same.
4. None of these.

Q. Contact angle of different liquids on pure glass surface are ${\theta }_1,{\theta }_2$ and ${\theta }_3$ and their wettability are represented as $w_1,w_2$ and $w_3$ respectively. If ${\theta }_1>{\theta }_2>{\theta }_3$, then

1. $w_1>w_2>w_3$
2. $w_1<w_2<w_3$
3. $w_1=w_2=w_3$
4. None of these

Q. Work of $3.0\times {10}^{-4}$ joule is required to be done in increasing the size of a soap film from $10cm\times 6cm$ to $10cm\times 11cm$. The surface tension of the film is

1. $5\times {10}^{-2}N/m$
2. $3\times {10}^{-2}N/m$
3. $1.5\times {10}^{-2}N/m$
4. $1.2\times {10}^{-2}N/m$

Q. The unit of surface tension in the $\text{CGS}$ system is

1. $\text{N/m}$
2. $\text{kg/cm}$
3. $\text{dyne/cm}$
4. $\text{dyne/m}$

Q. A $10\text{cm}$ long wire is placed horizontal on the surface of water and is gently pulled up with a force of $2\times {10}^{-2}\text{N}$ to keep the wire in equilibrium. The surface tension (in ${\text{Nm}}^{-1}$) of water is

1. $0.1$
2. $0.2$
3. $0.001$
4. $0.002$

Q. A cubical beaker of edge length $10\text{cm}$ is filled with a liquid of surface tension $0.075\text{N/m}$. Force across an imaginary diagonal on the surface of the liquid is

1. $\frac{3}{\sqrt{2}}\times {10}^{-2}\text{N}$
2. $\frac{3}{2}\times {10}^{-2}\text{N}$
3. $\frac{3}{2\sqrt{2}}\times {10}^{-2}\text{N}$
4. $3\times {10}^{-2}\text{N}$

Q. A soap bubble, having radius of $2\text{mm}$, is blown from a detergent solution having a surface tension of $5\times {10}^{-2}\text{N/m}$. Pressure inside the soap bubble is observed to be the same as the pressure at a point $h$ below the free surface of water taken in a container. Find the value of $h$.
[Take $g=10{\text{m/s}}^2$]

1. $2\text{cm}$
2. $4\text{cm}$
3. $3\text{cm}$
4. $1\text{cm}$

Q. A $10\text{cm}$ long wire is placed horizontal on the surface of water and is gently pulled up with a force of $2\times {10}^{-2}\text{N}$ to keep the wire in equilibrium. The surface tension (in ${\text{Nm}}^{-1}$) of water is

1. $0.1$
2. $0.2$
3. $0.001$
4. $0.002$

Q. A cubical beaker of edge length $10\text{cm}$ is filled with a liquid of surface tension $0.075\text{N/m}$. Force across an imaginary diagonal on the surface of the liquid is

1. $\frac{3}{\sqrt{2}}\times {10}^{-2}\text{N}$
2. $\frac{3}{2}\times {10}^{-2}\text{N}$
3. $\frac{3}{2\sqrt{2}}\times {10}^{-2}\text{N}$
4. $3\times {10}^{-2}\text{N}$

Q. Angle of contact of water on an oily surface is :

1. Acute
2. Obtuse
3. ${90}^{\circ }$
4. $0^{\circ }$

Q. When there is no external force, the shape of a small liquid drop is determined by

1. density of liquid
2. viscosity of air
3. surface tension
4. elasticity of liquid