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Surface Tension Multiple Choice Questions and Answers

1. At the critical temperature, the surface tension of the liquid
  1. Is zero
  2. Is infinity
  3. Is the same as that at the other temperature
  4. Cannot be determined

Answer: Is zero

2. Diameters of 2 water drops are 1 cm and 1.5 cm respectively. Find the ratio of excess pressures inside them.
  1. 1 ∶ 1
  2. 5 ∶ 3
  3. 3 ∶ 2
  4. More than one of the above

Answer: 3 ∶ 2

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3. Hairs of shaving brush cling together when it is removed from water due to
  1. Force of attraction between hairs
  2. Surface tension
  3. Viscosity of water
  4. Characteristic property of hairs

Answer: Surface tension

4. Surface energy is ________________
  1. kinetic energy of the surface molecules
  2. the force per unit length acting on surface particles
  3. the energy of the molecules inside the beaker
  4. the extra energy that the molecules at the surface have relative to molecules inside the liquid

Answer: the extra energy that the molecules at the surface have relative to molecules inside the liquid

5. What is the value of pressure inside the bubble of radius 1cm, if the bubble is in water at a depth (H) of 1m? Assume atmospheric pressure to be 1atm, surface tension = 0.075N/m & density of water = 1000kg/m3.
  1. 110015 Pa
  2. 109985 Pa
  3. 26 atm
  4. 4 atm

Answer: 110015 Pa

6. The contact angle determines whether liquid will rise or get depressed along a solid surface. Select the correct statement regarding the same.
  1. If contact angle is found to be less than 90°, the liquid will have raise along the solid surface
  2. If contact angle is found to be greater than 90°, then liquid will have depressed along the solid surface
  3. Liquid always rises along solid surface, irrespective of contact angle
  4. Liquid always gets depressed along solid surface, irrespective of contact angle

Answer: If contact angle is found to be less than 90°, the liquid will have raise along the solid surface

7. If T is the surface tension of the soap solution, the amount of work done in blowing a soap bubble from diameter D to a diameter 2D is
  1. 2πD2T
  2. 4πD2T
  3. 6πD2T
  4. 8πD2T

Answer: 6πD2T

8. In a surface tension experiment with a capillary tube, the water rises up to 0.1m. If the same experiment is repeated on an artificial satellite which is revolving around the earth. The rise of water in a capillary tube is
  1. 0.1 m
  2. 9.8 m
  3. 0.98 m
  4. Full length of the capillary tube

Answer: Full length of the capillary tube

9. A drop of oil is placed on the surface of the water. Which of the following statements is correct?
  1. It will remain on it as a sphere
  2. It will spread as a thin layer
  3. It will partly be as spherical droplets and partly as thin films
  4. It will float at the distorted drop on the water surface..

Answer: It will spread as a thin layer

10. The average radius of a soap bubble is 0.004 m. Find the excess pressure inside the soap bubble if the surface tension of soap bubble is 12 N/m.
  1. 0.048 Pa
  2. 0.050 Pa
  3. 12 KPa
  4. More than one of the above

Answer: 12 KPa

11. Why can insects move on the surface of water without sinking?
  1. Due to dynamic lift
  2. Due to the viscosity of water
  3. Due to the surface tension of water
  4. Due to the buoyant force

Answer: Due to the surface tension of water

12. A soap bubble contains two surface layers. What is the excess pressure just inside the first layer when seen from outside the bubble?
  1. 2S/R
  2. 4S/R
  3. -2S/R
  4. -4S/R

Answer: 2S/R

13. If the surface of a liquid is plane, then the angle of contact of the liquid with the walls of the container is
  1. Acute angle
  2. Obtuse angle
  3. 90°
  4. 0°

Answer: 0°

14. If a liquid does not wet a solid surface, then its angle of contact is:
  1. acute angle
  2. obtuse angle
  3. right angle
  4. More than one of the above

Answer: obtuse angle

15. Surface tension is due to :
  1. cohesive molecular forces
  2. gravitational forces
  3. nuclear forces
  4. electrical forces

Answer: cohesive molecular forces

16. Consider a spherical drop of liquid having radius ‘R’. Assume a diametric cross-section which divides the drop into two hemispheres. The hemispheres pull each other due to surface tension along the circumference of the diametrical cross-section. What is the value of this force?
  1. 2πRS
  2. πR2 S
  3. 2RS
  4. 0

Answer: 2πRS

17. When there are no external forces, the shape of a liquid drop is determined by
  1. Surface Tension of the liquid
  2. The density of the liquid
  3. The viscosity of the liquid
  4. The temperature of air only

Answer: Surface Tension of the liquid

18. If common salt is dissolved in water, then the surface tension of saltwater is
  1. Increased
  2. Decreased
  3. Not changed
  4. First increases then decrease

Answer: Increased

19. Which type of fluids have zero surface tension?
  1. Real fluids
  2. Ideal fluids
  3. Both ideal and real fluids
  4. No fluids have zero surface tension

Answer: Ideal fluids

20. Raindrops are spherical in shape because of
  1. Capillary
  2. Surface Tension
  3. Downward motion
  4. Acceleration due to gravity

Answer: Surface Tension

21. Excess pressure in a soap bubble of radius r is proportional to
  1. 1/r
  2. 1r2
  3. r
  4. More than one of the above

Answer: 1/r

22. Human hair cling together when it is removed from water due to
  1. Force of attraction between hairs
  2. Surface tension
  3. Viscosity of water
  4. Characteristic property of hairs

Answer: Surface tension

23. What will be the change in surface energy when a drop of liquid (S = 0.08N/m) is divided into 10 equal droplets? Radius of initial single drop (R)= 5cm.
  1. 0.1259 J
  2. 0.1141 J
  3. 0.2356 J
  4. 0.1765 J

Answer: 0.1141 J

24. When a soap bubble is charged
  1. It contracts
  2. It expands
  3. It does not undergo any change in size
  4. None of these

Answer: It expands

25. The surface of the water in contact with the glass wall is
  1. Plane
  2. Concave
  3. Convex
  4. Both 1 and 2

Answer: Concave

26. Work done in blowing the soap bubble in the air of radius 2R is W. Find the work done in blowing the soap bubble of radius R.
  1. 2W
  2. 4W
  3. W/2
  4. W/4

Answer: W/4

27. A capillary tube of diameter 2 mm is dipped in a liquid of specific gravity 0.8. The liquid rises in tube by 15 mm making an angle of contact of zero with the tube. Determine the surface tension of the liquid in contact with air and glass tube.
  1. 1 kN/m
  2. 0.05 kN/m
  3. 0.06 N/m
  4. More than one of the above

Answer: 0.06 N/m

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