1. When the surface area of a liquid increases, the surface energy of the liquid generally
A.
decreases
B.
increases
C.
becomes zero
D.
remains unchanged
Correct Answer:
increases
Explanation:
Surface energy is proportional to the area of the free surface. Therefore, increasing the surface area increases the surface energy.
2. The work required to increase the surface area of a liquid by area ΔA is equal to
A.
γΔA
B.
γ/ΔA
C.
ΔA/γ
D.
γ + ΔA
Correct Answer:
γΔA
Explanation:
For a liquid surface, the increase in surface energy, and hence the work done, is W = γΔA, where γ is the surface tension.
3. A liquid rises in a narrow capillary tube mainly because its surface tends to
A.
increase its gravitational energy
B.
minimize its surface energy
C.
increase its temperature
D.
remove all cohesion
Correct Answer:
minimize its surface energy
Explanation:
Capillary action occurs because the liquid surface rearranges itself to reduce surface energy, subject to adhesive and cohesive forces.
4. For a liquid that wets the walls of a capillary tube, the liquid surface near the wall is
A.
convex
B.
flat in every case
C.
concave
D.
completely absent
Correct Answer:
concave
Explanation:
A wetting liquid forms a concave meniscus. This shape is associated with the capillary rise produced by surface tension.
5. If the surface tension of a liquid is γ, the increase in surface energy when its free surface area increases by A is
A.
A/γ
B.
γA
C.
γ + A
D.
γ - A
Correct Answer:
γA
Explanation:
Surface energy change is given by ΔE = γΔA. With an area increase A, the change is γA.
6. In capillary rise, the surface energy of the liquid changes because the
A.
area of the liquid surface changes
B.
mass of the liquid disappears
C.
density becomes zero
D.
liquid stops experiencing gravity
Correct Answer:
area of the liquid surface changes
Explanation:
Capillary phenomena involve changes in liquid surface area and shape, so the surface energy changes according to ΔE = γΔA.
7. A liquid has surface tension 0.05 N/m. What work is needed to increase its surface area by 2 m²?
A.
0.025 J
B.
0.10 J
C.
2.5 J
D.
40 J
Correct Answer:
0.10 J
Explanation:
The work required is W = γΔA = 0.05 × 2 = 0.10 J.
8. The SI unit of surface energy per unit area is
A.
N/m
B.
N·m
C.
J/m²
D.
kg/m³
Correct Answer:
J/m²
Explanation:
Surface energy per unit area is measured in J/m². This is numerically equivalent to N/m, the unit of surface tension.
9. A soap film has two free surfaces. If each surface has area A and surface tension γ, its total surface energy is
A.
γA
B.
2γA
C.
γ/A
D.
A/(2γ)
Correct Answer:
2γA
Explanation:
A soap film has two surfaces, and each contributes γA to the surface energy. Thus, total surface energy is 2γA.
10. When a liquid rises in a capillary tube, its surface energy is related to the work done in
A.
creating or changing the liquid surface
B.
changing the atomic mass of the liquid
C.
destroying gravity
D.
changing the colour of the liquid
Correct Answer:
creating or changing the liquid surface
Explanation:
The work involved in capillary phenomena is connected with the change in surface energy caused by changing the liquid surface area.
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