physics : class11 Surface Tension and Surface Area : Surface Tension : Properties of Bulk Matter MCQ Questions and Answers
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Surface Tension and Surface Area
MCQ questions and answers.
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MCQ Questions
1. For a liquid surface under surface tension, which change generally requires work to be done against surface tension?
A.
Decreasing the surface area
B.
Increasing the surface area
C.
Keeping the surface area constant
D.
Removing the liquid completely
Correct Answer:
Increasing the surface area
Explanation:
Surface tension tends to reduce the surface area of a liquid. Therefore, work must be done against it to increase the surface area.
2. A liquid surface has surface tension T. If its area is increased by ΔA, the work done is equal to:
A.
T/ΔA
B.
ΔA/T
C.
TΔA
D.
T + ΔA
Correct Answer:
TΔA
Explanation:
The work required to increase the surface area of a liquid by ΔA is W = TΔA, where T is the surface tension.
3. Why does a small liquid drop tend to become spherical?
A.
A sphere has maximum surface area
B.
A sphere has minimum surface area for a given volume
C.
A sphere has no surface tension
D.
A sphere always has zero volume
Correct Answer:
A sphere has minimum surface area for a given volume
Explanation:
Surface tension tries to minimize the surface area. For a fixed volume, a sphere has the smallest possible surface area.
4. When several small liquid drops combine to form one larger drop, the total surface area generally:
A.
Increases
B.
Decreases
C.
Remains exactly zero
D.
Becomes infinite
Correct Answer:
Decreases
Explanation:
Combining drops reduces the total surface area. This is favored by surface tension, which tends to minimize the surface area.
5. When a large liquid drop breaks into many smaller drops, its total surface area generally:
A.
Decreases
B.
Increases
C.
Remains unchanged in every case
D.
Becomes zero
Correct Answer:
Increases
Explanation:
For the same total volume, many small drops have a greater total surface area than one large drop.
6. The surface energy of a liquid surface is directly proportional to its:
A.
Surface area
B.
Mass only
C.
Volume only
D.
Density only
Correct Answer:
Surface area
Explanation:
Surface energy is given by E = T A, so for a liquid with fixed surface tension, it is directly proportional to the surface area.
7. A soap film has two surfaces. If the area of each surface increases by ΔA, the work done is:
A.
TΔA
B.
2TΔA
C.
TΔA/2
D.
2ΔA/T
Correct Answer:
2TΔA
Explanation:
A soap film has two surfaces, so the total increase in area is 2ΔA. Thus, the work done is W = T(2ΔA) = 2TΔA.
8. If the surface area of a liquid is doubled while its surface tension remains constant, its surface energy becomes:
A.
Half
B.
Unchanged
C.
Double
D.
Four times
Correct Answer:
Double
Explanation:
Since surface energy E = T A, doubling the area doubles the surface energy when surface tension is constant.
9. A liquid tends to form a shape with the smallest possible surface area because surface tension:
A.
Increases surface energy
B.
Minimizes surface energy
C.
Eliminates the liquid volume
D.
Makes the liquid weightless
Correct Answer:
Minimizes surface energy
Explanation:
Surface energy is proportional to surface area. Surface tension causes the liquid to minimize its surface area and hence minimize its surface energy.
10. A rectangular liquid surface has its area increased by 0.02 m². If its surface tension is 0.05 N/m, the work done is:
A.
0.001 J
B.
0.01 J
C.
0.025 J
D.
1 J
Correct Answer:
0.001 J
Explanation:
Using W = TΔA, W = 0.05 × 0.02 = 0.001 J. The work is required to increase the surface area against surface tension.
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