CBSE Class 11 Surface Tension Worksheet A

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Question. A beaker with a liquid of density 1.4 g cm^–3 is in balance over one pan of a weighing machine. If a solid of mass 10 g and density 8 g cm^–3 is now hung from the top of that pan with a thread and sinking fully in the liquid without touching the bottom, the extra weight to be put on the other pan for balance will be
(a) 10.0 g
(b) 8.25 g
(c) 11.75 g
(d) –1.75 g

Answer: A

Question. There is a hole in the bottom of tank having water. If total pressure at bottom is 3 atm (1 atm = 10⁵ N/m²) then the velocity of water flowing from hole is
(a) √400m/s
(b) √600m/s
(c) √60m/s
(d) None of these

Answer: A

Question. A fast train goes past way side station platform at high speed. A person standing at the edge of the platform is
(a) attracted to train
(b) repelled from train
(c) unaffected by outgoing train
(d) affected only if the train's speed is more than the speed of sound

Answer: A

Question. Three tubes X, Y and Z are connected to a horizontal pipe in which ideal liquid is flowing. The radii of the tubes X, Y and Z at the junction are respectively 3 cm, 1 cm and 3 cm. It can be said 
(a) the height of the liquid in the tube A is maximum.
(b) the height of liquid in the tubes Aand B is same.
(c) the height liquid in the tubes A,B and C is same.
(d) the height of the liquid in the tubes A and C is the same.

Answer: D

Question. A sphere of brass released in a long liquid column attains a terminial speed v₀. If the terminal speed attained by sphere of marble of the same radius and released in the same liquid is nv₀, then the value of n will be (Given : The specific gravities of brass, marbles and the liquid are 8.5, 2.5 and 0.8 respectively.)
(a) 5/17
(b) 17/77
(c) 11/31
(d) 17/5

Answer: B

Question. Two pieces of metals are suspended from the arms of a balance and are found to be in equilibrium when kept immersed in water. The mass of one piece is 32 g and its density 8 g cm^–3. The density of the other is 5 g per cm³. Then the mass of the other is
(a) 28 g
(b) 35 g
(c) 21 g
(d) 33.6 g

Answer: B

Question. Water is flowing through a horizontal pipe having a restriction, then
(a) pressure will be greater at the restriction.
(b) pressure will be greater in the wider portion.
(c) pressure will be same throughout the length of the pipe.
(d) None of these

Answer: B

Question. A cylinder of height 20m is completely filled with water. The velocity of efflux of water (in ms^–1) through a small hole on the side wall or the cylinder near its bottom is
(a) 10 m/s
(b) 20 m/s
(c) 25.5 m/s
(d) 5 m/s

Answer: B

Question. A capillary tube of radius r is immersed in a liquid. The liquid rises to a height h. The corresponding mass is m. What mass of water shall rise in the capillary if the radius of the tube is doubled?
(a) m
(b) 2m
(c) 3m
(d) 4m

Answer: B

Question. A tank has a small hole at its botom of area of cross-section a. Liquid is being poured in the tank at the rate Vm³/s, the maximum level of liquid in the container will be (Area of tank A)
(a) V/gaA
(b) V²/2gAa
(c) V²/gAa
(d) V/2gaA

Answer: B

Question. The wetability of a surface by a liquid depends primarily on
(a) surface tension 
(b) density
(c) angle of contact between the surface and the liquid
(d) viscosity

Answer: C

Question. A fluid is in streamline flow across a horizontal pipe of variable area of cross section. For this which of the following statements is correct? 
(a) The velocity is minimum at the narrowest part of the pipe and the pressure is minimum at the widest part of the pipe
(b) The velocity is maximum at the narrowest part of the pipe and pressure is maximum at the widest part of the pipe
(c) Velocity and pressure both are maximum at the narrowest part of the pipe
(d) Velocity and pressure both are maximum at the widest part of the pipe

Answer: B

Question. A certain number of spherical drops of a liquid of radius ‘r’ coalesce to form a single drop of radius ‘R’ and volume ‘V’. If ‘T’ is the surface tension of the liquid, then :
(a) energy = 4VT (1/r - 1/R) is released
(b) energy = 3VT (1/r + 1/R) is released
(c) energy = 3VT (1/r - 1/R) is released
(d) energy is neither released nor absorbed

Answer: C

Question. A wind with speed 40 m/s blows parallel to the roof of a house. The area of the roof is 250 m². Assuming that the pressure inside the house is atmospheric pressure, the force exerted by the wind on the roof and the direction of the force will be (rair = 1.2 kg/m³) 
(a) 4.8 × 10⁵ N, upwards
(b) 2.4 × 10⁵ N, upwards
(c) 2.4 × 10⁵ N, downwards
(d) 4.8 × 10⁵ N, downwards

Answer: B

Question. A tall cylinder is filled with viscous oil. A round pebble is dropped from the top with zero initial velocity. From the plot shown in figure, indicate the one that represents the velocity (v) of the pebble as a function of time (t) . 

Answer: C

Question. The angle of contact at the interface of water-glass is 0°, ethyl alcohol-glass is 0°, mercury-glass is 140° and methyliodide-glass is 30°. A glass capillary is put in a trough containing one of these four liquids. It is observed that the meniscus is convex. The liquid in the trough is
(a) water
(b) ethylalcohol
(c) mercury
(d) methyliodide

Answer: C

Question. The cylindrical tube of a spray pump has radius, R, one end of which has n fine holes, each of radius r. If the speed of the liquid in the tube is V, the speed of the ejection of the liquid through the holes is :
(a) VR²/nr²
(b) VR²/n³ r²
(c) VR²/nr
(d) VR²/n² r²

Answer: A

Question. A water tank of height 10m, completely filled with water is placed on a level ground. It has two holes one at 3 m and the other at 7 m from its base. The water ejecting from
(a) both the holes will fall at the same spot
(b) upper hole will fall farther than that from the lower hole
(c) upper hole will fall closer than that from the lower hole
(d) more information is required

Answer: A

Question. Two drops of the same radius are falling through air with a steady velocity of 5 cm per sec. If the two drops coalesce, the terminal velocity would be
(a) 10 cm per sec
(b) 2.5 cm per sec
(c) 5 × (4)^1/3 cm per sec
(d) 5 x √3 cm per sec

Answer: C

Directions for Each question contains STATEMENT-1 and STATEMENT-2.
Choose the correct answer from the following-
(a) Statement -1 is false, Statement-2 is true
(b) Statement -1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1
(c) Statement -1 is true, Statement-2 is true; Statement -2 is not a correct explanation for Statement-1
(d) Statement -1 is true, Statement-2 is false

Question. Statement 1 : The velocity of flow of a liquid is smaller when pressure is larger and vice-versa.
Statement 2 : According to Bernoulli’s theorem, for the stream line flow of an ideal liquid, the total energy per unit mass remains constant.

Answer: A

Question. Statement 1 : The buoyant force on a submerged rigid object can be considered to be acting at the centre of mass of the object.
Statement 2 : For a rigid body a force field distributed uniformly through its volume can be considered to be acting at the centre of mass of the body.

Answer: D

Question. Statement 1 : Falling raindrops acquire a terminal velocity.
Statement 2 : A constant force in the direction of motion and a velocity dependent force opposite to the direction of motion, always result in the acquisition of terminal velocity.

Answer: A

Question. Statement 1 : Smaller the droplets of water, spherical they are.
Statement 2 : Force of surface tension is equal, and opposite to force of gravity.

Answer: C

Question. Statement 1 : If a body is floating in a liquid, the density of liquid is always greater than the density of solid.
Statement 2 : Surface tension is the property of liquid surface.

Answer: D

1. Oil is sprinkled on sea waves to calm them. Why?

2. A drop of oil placed on the surface of water spreads out, but a drop of water placed on oil contracts. Why?

3. Water rises in a capillary tube but mercury falls in the same tube. Why?

4. What should be the pressure inside a small air bubble of 0.1mm radius situated just below the water surface? Surface tension of water = 7.2 × 10^-2 N/m and atmospheric pressure = 1.013 × 10⁵ N/m²?

5. Why is a soap solution a better cleansing agent than ordinary water?

6. The antiseptics used for cuts and wounds in human flesh have low surface tension. Why?                                     

7. If the radius of a soap bubble is r and surface tension of the soap solution is T. Keeping the temperature constant, what is the extra energy needed to double the radius of soap bubble?

8. Find the work done in breaking a water drop of radius 1 mm into 1000 drops. Given the surface tension of water is 72 × 10^-3 N/m?

9. What is the energy stored in a soap babble of diameter 4 cm, given the surface tension = 0.07 N/m?

10. What is the work done in splitting a drop of water of 1 mm radius into 64 droplets? Given the surface tension of water is 72 × 10^-3 N/m²?

11. Why should detergents have small angles of contact?

12. Show that if two soap bubbles of radii a and b coalesce to from a single bubble of radius c. If the external pressure is P, show that the surface tension T of soap      

Click on link below to download CBSE Class 11 Surface Tension Worksheet A.