Surface tension, capillarity, drops and bubbles - Question Bank

1. Surface tension can be reduced by:
A) Increasing temperature.
B) Adding soluble impurities like salt.
C) Adding insoluble impurities like dust.
D) Increasing pressure.
2. If two soap bubbles of radii r1 and r2 (r1 > r2) are joined by a tube, then air will flow from:
A) The smaller bubble to the larger bubble.
B) The larger bubble to the smaller bubble.
C) There will be no flow of air.
D) It depends on the temperature difference.
3. Which of the following is a consequence of surface tension?
A) Formation of spherical raindrops.
B) Capillary rise.
C) Floating of a needle on water.
D) All of the above.
4. The rise of liquid in a capillary tube is independent of:
A) Surface tension
B) Angle of contact
C) Radius of the tube
D) Density of the liquid
5. A liquid will not wet a solid surface if:
A) Cohesive forces are greater than adhesive forces.
B) Adhesive forces are greater than cohesive forces.
C) Surface tension is zero.
D) The angle of contact is zero.
6. The excess pressure in a liquid film stretched between two surfaces is:
A) 2T/r
B) 4T/r
C) T/r
D) 0
7. The pressure at the bottom of a liquid drop is:
A) Uniform throughout the drop.
B) Maximum at the center.
C) Minimum at the center.
D) Depends on the atmospheric pressure.
8. If the angle of contact is obtuse, the liquid:
A) Wets the solid surface.
B) Does not wet the solid surface.
C) Forms a concave meniscus.
D) Has low cohesive forces.
9. If the angle of contact is acute, the liquid:
A) Wets the solid surface.
B) Does not wet the solid surface.
C) Forms a convex meniscus.
D) Has high cohesive forces.
10. What is the work done to expand a spherical soap bubble of radius R to radius 2R?
A) 6πR²T
B) 4πR²T
C) 2πR²T
D) 8πR²T
11. The force tending to minimize the surface area of a liquid is called:
A) Surface tension
B) Surface energy
C) Cohesion
D) Adhesion
12. A man can float on water due to:
A) Surface tension
B) Buoyancy
C) His low density compared to water
D) Both B and C
13. If the temperature of a liquid decreases, its surface tension generally:
A) Increases
B) Decreases
C) Remains the same
D) Becomes zero
14. The angle of contact between a liquid and a solid surface depends on:
A) The nature of the liquid and the solid.
B) The cleanliness of the surfaces.
C) The medium between the liquid and the solid.
D) All of the above.
15. A capillary tube is inserted into a liquid. The liquid level in the tube is lower than the outside level. This indicates:
A) The liquid wets the tube.
B) The liquid does not wet the tube.
C) The surface tension is very high.
D) The density of the liquid is very low.
16. If the surface tension of water is 0.07 N/m, the excess pressure in a small air bubble of radius 0.1 mm inside water is:
A) 1.4 Pa
B) 0.7 Pa
C) 1400 Pa
D) 700 Pa
17. What is the shape of a small air bubble inside a liquid?
A) Spherical
B) Elliptical
C) Cylindrical
D) Flat
18. Which of the following factors does NOT affect the surface tension of a liquid?
A) Nature of the liquid
B) Temperature
C) Presence of impurities
D) Volume of the liquid
19. The surface tension of a liquid is the energy stored in the surface per unit:
A) Area
B) Volume
C) Length
D) Mass
20. A clean glass plate is dipped in mercury and is then withdrawn. The surface of mercury on the plate will be:
A) Concave upwards
B) Convex upwards
C) Flat
D) Irregular
21. If a liquid surface is extended by pulling it apart, work is done against:
A) Cohesive forces
B) Adhesive forces
C) Gravitational forces
D) Viscous forces
22. The work done in forming a spherical drop of radius R from the material of the liquid is:
A) 4πR²T
B) 2πRT
C) 8πRT
D) 4πRT
23. Consider a large soap bubble and a small soap bubble in contact. The surface of contact between them will be:
A) Concave towards the larger bubble.
B) Concave towards the smaller bubble.
C) Flat.
D) Cylindrical.
24. A liquid drop of radius R has a certain surface energy. If it breaks into 8 identical smaller drops, what is the change in surface energy?
A) It increases.
B) It decreases.
C) It remains the same.
D) It depends on the liquid.
25. The excess pressure inside a bubble is zero if:
A) Surface tension is zero.
B) Radius is infinite.
C) Both A and B are true.
D) It is not possible for excess pressure to be zero.
26. If the radius of a capillary tube is doubled, the capillary rise will be:
A) Doubled
B) Halved
C) Four times
D) One-fourth
27. The phenomenon of capillarity is utilized in:
A) Lifting oil in a kerosene lamp.
B) Drying of clothes.
C) Absorption of ink by a blotting paper.
D) All of the above.
28. Which of the following statements about surface tension is FALSE?
A) It is a scalar quantity.
B) It is independent of the area of the surface.
C) It decreases with increasing temperature.
D) It is measured in N/m.
29. When a needle is carefully placed on the surface of still water, it floats. This is an example of:
A) Surface tension
B) Buoyancy
C) Density difference
D) Adhesion
30. The force acting on a unit length of a line drawn on the surface of a liquid is equal to:
A) Surface tension
B) Surface energy
C) Pressure
D) Viscosity
31. A liquid film on a loop of any shape tends to assume a shape that minimizes:
A) Surface area
B) Volume
C) Mass
D) Density
32. Work done in increasing the surface area of a liquid film by 'dA' is given by:
A) T * dA
B) 2T * dA
C) T / dA
D) dA / T
33. If two soap bubbles of radii r1 and r2 coalesce, the radius of the new bubble r is given by:
A) r = sqrt((r1³ + r2³)/(r1 + r2))
B) r = (r1 + r2)/2
C) r = sqrt(r1² + r2²)
D) r = (r1³ + r2³)/(r1² + r2²)
34. Why is the excess pressure inside a soap bubble (4T/r) twice that of a liquid drop (2T/r) of the same radius?
A) A soap bubble has two free surfaces, while a drop has only one.
B) The liquid in a bubble is less dense than in a drop.
C) The temperature inside the bubble is higher.
D) The surfactant in the bubble increases surface tension.
35. What is the excess pressure inside a spherical soap bubble compared to the atmospheric pressure?
A) 4T/r
B) 2T/r
C) T/r
D) T/(2r)
36. The pressure inside a spherical liquid drop is greater than the atmospheric pressure by an amount equal to:
A) 2T/r
B) T/r
C) 4T/r
D) T/(2r)
37. What causes a liquid drop to be spherical in shape?
A) Surface tension, which minimizes surface area.
B) Gravity, which pulls the liquid downwards.
C) Viscosity, which resists deformation.
D) Evaporation, which causes shrinkage.
38. If a capillary tube is dipped in water and then lifted, the water column will break if the height of the tube is greater than the capillary rise.
A) True
B) False
C) Depends on the diameter of the tube
D) Depends on the density of water
39. For mercury in a glass capillary tube, the angle of contact is approximately 140 degrees. Therefore, cos θ is approximately:
A) 0.64
B) -0.64
C) 0.34
D) -0.34
40. For water in a glass capillary tube, the angle of contact is approximately 0 degrees. Therefore, cos θ is approximately:
A) 1
B) 0
C) -1
D) 0.5
41. The height 'h' of capillary rise of a liquid of surface tension 'T' in a tube of radius 'r' is given by the formula (where θ is the angle of contact and ρ is the density):
A) h = (2T cos θ) / (ρgr)
B) h = (T cos θ) / (2ρgr)
C) h = (2T sin θ) / (ρgr)
D) h = (T sin θ) / (2ρgr)
42. The rise of water in a capillary tube is inversely proportional to:
A) The radius of the tube.
B) The density of the liquid.
C) The surface tension of the liquid.
D) The angle of contact.
43. In a capillary tube, if the liquid does not wet the walls (e.g., mercury in glass), the meniscus is:
A) Concave
B) Convex
C) Flat
D) Elliptical
44. In a capillary tube, if the liquid wets the walls (e.g., water in glass), the meniscus is:
A) Concave
B) Convex
C) Flat
D) Cylindrical
45. Capillarity is the phenomenon of rise or fall of a liquid in a narrow tube. This is due to:
A) Surface tension and adhesive forces.
B) Viscosity and density.
C) Pressure difference and gravity.
D) Cohesive forces only.
46. What is the effect of adding a surfactant (like soap) to water on its surface tension?
A) Surface tension increases significantly.
B) Surface tension decreases significantly.
C) Surface tension remains unchanged.
D) Surface tension becomes negative.
47. How does temperature affect surface tension?
A) Surface tension increases with increasing temperature.
B) Surface tension decreases with increasing temperature.
C) Temperature has no effect on surface tension.
D) Surface tension becomes zero at absolute zero.
48. Which intermolecular force is primarily responsible for surface tension in liquids?
A) Hydrogen bonding
B) Van der Waals forces
C) Ionic bonding
D) Covalent bonding
49. What is the SI unit of surface tension?
A) Newton per meter (N/m)
B) Joule per meter squared (J/m²)
C) Pascal (Pa)
D) Newton meter (N·m)
50. What is surface tension?
A) The tendency of liquid surfaces to shrink into the minimum surface area possible.
B) The force that holds molecules together in a solid.
C) The pressure exerted by a gas on its container.
D) The resistance of a liquid to flow.
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