Surface Tension

Q. 13. The force between two point charges in air is100 N. If the distance between them is increasedby 50%, then the force between two charges willbe nearly equal to(1) 50 N(3) 100 N(2) 56 N(4) 44 N

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.

The breaking stress of a wire depends upon the:

1. Length of the wire

2. Radius of the wire

3. Material of the wire

4. Shape of the cross-section

Q.

Define angle of contact.

Q. At what height above the surface of earth the value of $g$ decreases by $2\%$ ?
$($radius of the earth is $6400\text{km})$

1. $32\text{km}$
2. $64\text{km}$
3. $128\text{km}$
4. $1600\text{km}$

Q. A gas bubble from an explosion under water oscillates with a time period T which depends upon static pressure p, density of water $\rho$ and the total energy of explosion E. Find the expression for the time period T. (where, k is a dimensionless constant)

1. 
2. 
3. 
4. 

Q. A container filled with air under pressure $P_0$ contains a soap bubble of radius $R$. The air pressure has been reduced to half isothermally and the new radius of the bubble becomes $\frac{5R}{4}$. If the surface tension of the soap water solution is $S$, $P_0$ is found to be $\frac{nS}{R}$ SI unit, where $n$ is

Q. When water is filled carefully in a glass, one can fill it to a height $h$ above the rim of the glass due to the surface tension of water. To calculate $h$ just before water starts flowing, model the shape of the water above the rim as a disc of thickness $h$ having semicircular edges, as shown schematically in the figure. When the pressure of water at the bottom of this disc exceeds what can be withstood due to the surface tension, the water surface breaks near the rim and water starts flowing from there. If the density of water, its surface tension and the acceleration due to gravity are ${10}^3$ ${\text{kg/m}}^3$ , $0.07$ ${\text{Nm}}^{-1}$ and $10{\text{ms}}^{-2}$ , respectively, the value of $h$ (in mm) is

Q. The rain drops are in spherical shape due to

1. surface tension in drop
2. gravitational force on drop
3. air resistance on drop
4. thrust on drop

Q. Water enters a house through a pipe $2\text{cm}$ inside diameter at an absolute pressure $4\times {10}^5\text{Pa}$ (about $4$ atmospheres). The pipe leading to second floor bathroom $5\text{m}$ above is $1\text{cm}$ in diameter. The flow velocity at the inlet pipe is $4\text{m/s}$. The pressure in the bathroom.

1. $2\times {10}^5\text{Pa}$
2. $2.3\times {10}^5\text{Pa}$
3. $3\times {10}^5\text{Pa}$
4. $3.3\times {10}^5\text{Pa}$

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

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

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.

The contact angle between a solid and a liquid is a property of?

1. the material of the solid

2. the material of the liquid

3. the shape of the solid

4. the mass of the solid

Q. When a soap bubble is charged excess pressure inside it (assume radius does not change) 1) Decreases 2)Increases 3)Does not Change 4)Depends on the nature of cha

Q. Water is flowing in a horizontal pipe of non-uniform area of cross- section. The velocity of water at a place, where the radius of pipe is $0.01\text{m}$ is $25\text{m/s}$. What will be the velocity of water where the radius of pipe is $0.02\text{m}$?

1. None of these
2. $6.75\text{m/s}$
3. $6.25\text{m/s}$
4. $7.25\text{m/s}$

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 capillary tube made of glass of radius $0.15mm$ is dipped vertically in a beaker filled with methylene iodide (surface tension $=0.05N{m}^{-1}$, density $=667kg{m}^{-3}$) which rises to height $h$ in the tube. It is observed that the two tangents drawn from liquid-glass interfaces (from opp. sides of the capillary) make an angle of $60°$ with one another. Then $h$ is close to ($g=10m{s}^{-2}$).

1. $0.172m$

2. $0.049m$

3. $0.087m$

4. $0.137m$

Q. A large number of liquid drops each of radius $a$ coalesce to form a single spherical drop of radius $b$. The energy released in the process is converted into kinetic energy of the big drop formed. What will be the speed of the bigger drop, if it starts from rest?
[Given, $T$ is the surface tension and $\rho$ is the density of liquid]

1. $\sqrt{\frac{6T}{\rho }[\frac{1}{a}-\frac{1}{b}]}$
2. $\sqrt{\frac{4T}{\rho }[\frac{1}{a}-\frac{1}{b}]}$
3. $\sqrt{\frac{8T}{\rho }[\frac{1}{a}-\frac{1}{b}]}$
4. $\sqrt{\frac{5T}{\rho }[\frac{1}{a}-\frac{1}{b}]}$

Q. Water rises to a height of $16.3\text{cm}$ in a capillary of height $18\text{cm}$ above the water level. If the tube is cut at a height of $12\text{cm}$,

1. water will come out as a fountain from the capillary tube.
2. water will stay at a height of $12\text{cm}$ in the capillary tube but radius of curvature at the top will increase.
3. water will stay at a height of $12\text{cm}$ in capillary tube but radius of curvature at the top will decrease.
4. water will flow down the side of the capillary tube.

Q.

If the error in measurement of the surface area of a sphere is 4%, then the error in measurement of its volume will be

1. 4%
2. 6%
3. 8%
4. 16%

Q. A RCC beam ($250mm\times 500mm$ overall) is subjected to service working load of $20kN/m$. The span of beam is $6m$. The characteristic compressive strength of concrete is $20MPa$ and the characteristic strength of steel is $415MPa$. The effective cover to reinforcing bar of diameter $16mm$ is $25mm$. For balanced failure, number of bars (approximate value) required are:

1. 3
2. 4
3. 5
4. 6

Q.

The angle of contact between glass and mercury is

1. 30^o

2. 135^o

3. 90^o

4. 0°

Q.

Mercury has an angle of contact equal to ${140}^{\circ }$ with soda lime glass. A narrow tube of radius 1.00 mm made of this glass is dipped in a trough containing mercury. By what amount does the mercury dip down in the tube relative to the liquid surface outside? Surface tension of mercury at the temperature of the experiment is 0.465 N$m^{-1}$. Density of mercury = $13.6\times {10}^{3}kg{m}^{–3}$.

Q. A body weighs $w$ at the surface of the earth. Its weight at a height equal to half the radius of the earth will be:-

1. $\frac{w}{2}$
2. $\frac{2w}{3}$
3. $\frac{4w}{9}$
4. $\frac{9w}{27}$

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. 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.

What is cleavage property?

Q. The rise of a liquid in a capillary tube depends on

1. The material of the tube
2. The length of the tube
3. The outer raidus of the tube
4. The inner radius of the tube

Q.

What is the difference between tension and surface tension?

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

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