physics : class11 Wetting of Surfaces : Surface Tension : Properties of Bulk Matter MCQ Questions and Answers
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Wetting of Surfaces
MCQ questions and answers.
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MCQ Questions
1. A liquid is said to wet a solid surface when it spreads over the surface. Which condition generally favors wetting?
A.
Adhesion between liquid and solid is greater than cohesion within the liquid
B.
Cohesion within the liquid is greater than adhesion to the solid
C.
There is no attraction between the liquid and the solid
D.
The liquid has zero surface tension
Correct Answer:
Adhesion between liquid and solid is greater than cohesion within the liquid
Explanation:
Wetting occurs when the adhesive force between the liquid and solid is stronger than the cohesive force between liquid molecules.
2. What type of meniscus is formed by water in a clean glass tube?
A.
Convex
B.
Concave
C.
Flat
D.
Irregular
Correct Answer:
Concave
Explanation:
Water wets glass because adhesion between water and glass is strong, producing a concave meniscus.
3. What type of meniscus is formed by mercury in a clean glass tube?
A.
Concave
B.
Convex
C.
Flat
D.
Cylindrical
Correct Answer:
Convex
Explanation:
Mercury does not wet glass because its cohesive forces are stronger than its adhesive forces with glass, so it forms a convex meniscus.
4. The angle of contact for a liquid that completely wets a solid surface is approximately
A.
0 degrees
B.
45 degrees
C.
90 degrees
D.
180 degrees
Correct Answer:
0 degrees
Explanation:
For complete wetting, the liquid spreads over the solid and the angle of contact is approximately zero.
5. A liquid generally does not wet a solid surface when
A.
Adhesion is greater than cohesion
B.
Cohesion is greater than adhesion
C.
Adhesion and cohesion are both absent
D.
The liquid has no molecules
Correct Answer:
Cohesion is greater than adhesion
Explanation:
If cohesive forces within the liquid are stronger than adhesive forces between the liquid and solid, the liquid tends to avoid spreading and does not wet the surface.
6. Which of the following liquids wets clean glass?
A.
Water
B.
Mercury
C.
Liquid metal only
D.
A liquid with zero adhesion to glass
Correct Answer:
Water
Explanation:
Water wets clean glass because the adhesive force between water and glass is stronger than the cohesive force in water.
7. A liquid that spreads over a solid surface has an angle of contact that is generally
A.
Less than 90 degrees
B.
Greater than 90 degrees
C.
Exactly 180 degrees
D.
Always exactly 90 degrees
Correct Answer:
Less than 90 degrees
Explanation:
A wetting liquid has a small angle of contact, usually less than 90 degrees, indicating strong adhesion to the solid.
8. Why does water spread more easily on a clean glass surface than on a greasy glass surface?
A.
Water has stronger adhesion with clean glass
B.
Water has no surface tension on clean glass
C.
Grease increases water's adhesion to glass
D.
Clean glass contains no molecules
Correct Answer:
Water has stronger adhesion with clean glass
Explanation:
Water adheres strongly to clean glass, whereas a greasy layer reduces direct contact and weakens the wetting of glass by water.
9. Which statement about the angle of contact is correct for a non-wetting liquid on a solid surface?
A.
It is less than 30 degrees
B.
It is greater than 90 degrees
C.
It is always zero
D.
It cannot be measured
Correct Answer:
It is greater than 90 degrees
Explanation:
A non-wetting liquid forms a large angle of contact, generally greater than 90 degrees, because cohesion is stronger than adhesion.
10. Soap helps water spread over cloth mainly because it
A.
Improves the wetting of the cloth by water
B.
Removes all water molecules
C.
Makes water completely non-adhesive
D.
Changes water into a solid
Correct Answer:
Improves the wetting of the cloth by water
Explanation:
Soap improves the contact between water and the cloth, allowing water to wet and spread over the surface more easily.
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