physics : class11 Molecular Origin of Surface Tension : Surface Tension : Properties of Bulk Matter MCQ Questions and Answers
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Molecular Origin of Surface Tension
MCQ questions and answers.
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MCQ Questions
1. Why does a molecule inside a liquid experience nearly zero resultant intermolecular force?
A.
It has no intermolecular forces
B.
It is surrounded by molecules in all directions
C.
It has a very high temperature
D.
It is lighter than surface molecules
Correct Answer:
It is surrounded by molecules in all directions
Explanation:
A molecule inside the liquid is surrounded by neighboring molecules on all sides, so the cohesive forces acting on it nearly balance in every direction.
2. What is the main reason a liquid surface behaves like a stretched membrane?
A.
Surface molecules experience a net inward cohesive force
B.
Surface molecules have no intermolecular attraction
C.
Surface molecules are repelled equally in all directions
D.
Surface molecules are completely stationary
Correct Answer:
Surface molecules experience a net inward cohesive force
Explanation:
Surface molecules have fewer neighboring molecules above them, so the cohesive attraction from the liquid below produces a net force inward. This gives the surface a stretched-membrane-like behavior.
3. Compared with molecules in the interior of a liquid, surface molecules generally have:
A.
More neighboring molecules
B.
Fewer neighboring molecules
C.
No molecular attraction
D.
The same surroundings in every direction
Correct Answer:
Fewer neighboring molecules
Explanation:
A surface molecule is surrounded by liquid molecules mainly below and beside it, while there are fewer or no liquid molecules above it. Therefore, it has fewer neighboring molecules than an interior molecule.
4. The intermolecular attractive forces responsible for surface tension are commonly called:
A.
Cohesive forces
B.
Gravitational forces
C.
Magnetic forces
D.
Nuclear forces
Correct Answer:
Cohesive forces
Explanation:
Cohesive forces are attractive forces between molecules of the same liquid. Their unequal effect on surface molecules produces the molecular origin of surface tension.
5. Why do liquid surfaces tend to have minimum area?
A.
Surface molecules are pushed away from the liquid
B.
The liquid surface has excess molecular energy
C.
Interior molecules stop attracting one another
D.
Surface molecules become electrically neutral
Correct Answer:
The liquid surface has excess molecular energy
Explanation:
Surface molecules have higher potential energy because their cohesive interactions are not fully balanced. A liquid tends to reduce this excess surface energy by minimizing its surface area.
6. What happens to a molecule when it moves from the interior of a liquid to its surface?
A.
Its intermolecular potential energy generally increases
B.
Its intermolecular potential energy becomes zero
C.
Its mass decreases
D.
Its cohesive forces disappear completely
Correct Answer:
Its intermolecular potential energy generally increases
Explanation:
At the surface, the molecule has fewer neighboring molecules with which it can interact attractively. Hence, it is in a higher potential-energy state than a molecule inside the liquid.
7. The net cohesive force on a molecule at the liquid surface is directed mainly:
A.
Outward from the liquid
B.
Inward toward the liquid
C.
Vertically upward only
D.
Randomly in all directions
Correct Answer:
Inward toward the liquid
Explanation:
Because surface molecules have fewer neighbors above them, the attractive forces from molecules within the liquid are unbalanced and produce a net inward force.
8. Which molecular property of a liquid is directly associated with the origin of surface tension?
A.
Attraction between neighboring liquid molecules
B.
Repulsion between all liquid molecules
C.
Absence of molecular motion
D.
Equal molecular forces only at the surface
Correct Answer:
Attraction between neighboring liquid molecules
Explanation:
Surface tension originates from cohesive attraction between neighboring molecules. This attraction is balanced for interior molecules but unbalanced for molecules at the surface.
9. Why is a molecule at the surface in a different energy state from one inside the liquid?
A.
The surface molecule has fewer attractive neighbors
B.
The surface molecule has no mass
C.
The interior molecule has no kinetic energy
D.
The surface molecule is outside the influence of gravity
Correct Answer:
The surface molecule has fewer attractive neighbors
Explanation:
Fewer neighboring molecules means fewer attractive interactions for a surface molecule. Therefore, its molecular potential energy differs from that of an interior molecule.
10. Surface tension can be understood molecularly as a tendency of a liquid to:
A.
Increase the number of molecules at its surface
B.
Reduce the number of molecules in its interior
C.
Reduce its surface area due to cohesive attraction
D.
Eliminate all intermolecular forces
Correct Answer:
Reduce its surface area due to cohesive attraction
Explanation:
Cohesive forces pull surface molecules inward and make the surface possess excess energy. The liquid tends to minimize this energy by reducing its surface area.
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