physics : class11 Surface Energy in Bubble Formation : Surface Energy : Properties of Bulk Matter MCQ Questions and Answers
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Surface Energy in Bubble Formation
MCQ questions and answers.
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MCQ Questions
1. A soap bubble has how many liquid-air surfaces?
A.
One
B.
Two
C.
Three
D.
Four
Correct Answer:
Two
Explanation:
A soap bubble has a thin soap film with a liquid-air surface on both its inner and outer sides, so it has two surfaces.
2. If the surface tension of a soap solution is T and the radius of a soap bubble is r, what is its surface energy?
A.
4πTr²
B.
8πTr²
C.
2πTr²
D.
16πTr²
Correct Answer:
8πTr²
Explanation:
The total area of the two surfaces of a soap bubble is 2 × 4πr² = 8πr². Therefore, surface energy is T × 8πr² = 8πTr².
3. Why is the surface energy of a soap bubble twice that of a liquid drop of the same radius and surface tension?
A.
The bubble has twice the volume
B.
The bubble has two surfaces
C.
The bubble has twice the mass
D.
The bubble has twice the density
Correct Answer:
The bubble has two surfaces
Explanation:
A liquid drop has one free surface, whereas a soap bubble has inner and outer surfaces. Hence, the bubble has twice the surface energy for the same radius and surface tension.
4. The surface energy of a soap bubble is directly proportional to which quantity when surface tension is constant?
A.
Radius
B.
Square of radius
C.
Cube of radius
D.
Inverse of radius
Correct Answer:
Square of radius
Explanation:
The surface energy of a soap bubble is E = 8πTr². Thus, for constant surface tension, it is directly proportional to r².
5. What happens to the surface energy of a soap bubble if its radius is doubled, with surface tension unchanged?
A.
It becomes twice
B.
It becomes four times
C.
It becomes half
D.
It remains unchanged
Correct Answer:
It becomes four times
Explanation:
Since surface energy E = 8πTr², doubling the radius makes the energy proportional to (2r)² = 4r². Therefore, the surface energy becomes four times.
6. What is the work required to increase the radius of a soap bubble from r1 to r2, if its surface tension is T?
A.
4πT(r2² − r1²)
B.
8πT(r2² − r1²)
C.
2πT(r2 − r1)
D.
8πT(r2 − r1)
Correct Answer:
8πT(r2² − r1²)
Explanation:
The work required equals the increase in surface energy. Since E = 8πTr², the increase is 8πT(r2² − r1²).
7. If the surface tension of a soap solution is doubled while the bubble radius remains constant, its surface energy will become:
A.
Half
B.
Unchanged
C.
Twice
D.
Four times
Correct Answer:
Twice
Explanation:
Surface energy is E = 8πTr². For constant radius, energy is directly proportional to surface tension, so doubling T doubles the surface energy.
8. The surface energy of a soap bubble is calculated by multiplying surface tension by:
A.
The volume of the bubble
B.
The total area of both surfaces
C.
The radius of the bubble
D.
The pressure inside the bubble
Correct Answer:
The total area of both surfaces
Explanation:
Surface energy equals surface tension multiplied by the surface area. For a soap bubble, the relevant area is the combined area of its inner and outer surfaces.
9. A soap bubble of radius r has a total surface area equal to:
A.
4πr²
B.
8πr²
C.
2πr²
D.
16πr²
Correct Answer:
8πr²
Explanation:
Each spherical surface has area 4πr². Since a soap bubble has two surfaces, its total surface area is 2 × 4πr² = 8πr².
10. When a soap bubble expands, the work done in expansion is mainly stored as:
A.
Surface energy
B.
Gravitational energy
C.
Nuclear energy
D.
Magnetic energy
Correct Answer:
Surface energy
Explanation:
Expansion increases the area of both surfaces of the soap film. The work done in creating this additional area is stored as surface energy.
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Surface Energy in Bubble Formation
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