chemistry : class11 Excess Pressure in a Soap Bubble : Surface tension : States of Matter: Gases and Liquids MCQ Questions and Answers
Practice important
Excess Pressure in a Soap Bubble
MCQ questions and answers.
Page 1
of
1
|
10
MCQ Questions
1. A soap bubble has a radius of 2.0 mm and the surface tension of its solution is 3.0 × 10^-2 N m^-1. What is the excess pressure inside the bubble?
A.
15 Pa
B.
30 Pa
C.
60 Pa
D.
120 Pa
Correct Answer:
60 Pa
Explanation:
A soap bubble has two liquid surfaces, so its excess pressure is ΔP = 4T/r. Substituting T = 3.0 × 10^-2 N m^-1 and r = 2.0 × 10^-3 m gives ΔP = 4(3.0 × 10^-2)/(2.0 × 10^-3) = 60 Pa.
2. Two soap bubbles have radii r and 2r and are made of the same solution at the same temperature. What is the ratio of their excess pressures, ΔP_r : ΔP_2r?
A.
1 : 2
B.
2 : 1
C.
1 : 4
D.
4 : 1
Correct Answer:
2 : 1
Explanation:
For a soap bubble, ΔP = 4T/r. Since surface tension is the same, excess pressure is inversely proportional to radius. Therefore, ΔP_r/ΔP_2r = (1/r)/(1/2r) = 2, giving 2 : 1.
3. The radius of a soap bubble increases from 1.0 mm to 3.0 mm without any change in surface tension. How does its excess pressure change?
A.
It becomes three times its original value
B.
It becomes one-third of its original value
C.
It becomes one-ninth of its original value
D.
It remains unchanged
Correct Answer:
It becomes one-third of its original value
Explanation:
The excess pressure of a soap bubble is ΔP = 4T/r. With constant surface tension, increasing the radius from r to 3r changes the excess pressure from 4T/r to 4T/(3r), which is one-third of the original value.
4. Two soap bubbles of radii 2.0 mm and 3.0 mm are formed from a liquid whose surface tension is 2.5 × 10^-2 N m^-1. What is the difference between their internal pressures?
A.
8.33 Pa
B.
16.7 Pa
C.
25.0 Pa
D.
41.7 Pa
Correct Answer:
16.7 Pa
Explanation:
The pressure difference between the bubbles is the difference in their excess pressures: ΔP = 4T(1/r_1 − 1/r_2). Thus, ΔP = 4(2.5 × 10^-2)[1/(2.0 × 10^-3) − 1/(3.0 × 10^-3)] = 16.7 Pa. The smaller bubble has the higher pressure.
5. A soap bubble and an air bubble in water have the same radius and the same surface tension at the interface. What is the ratio of their excess pressures, soap bubble : air bubble?
A.
1 : 2
B.
1 : 1
C.
2 : 1
D.
4 : 1
Correct Answer:
2 : 1
Explanation:
A soap bubble has two liquid surfaces, so its excess pressure is 4T/r. An air bubble in a liquid has only one interface, so its excess pressure is 2T/r. Therefore, the ratio is (4T/r):(2T/r) = 2:1.
6. A soap bubble has an excess pressure of 100 Pa when the surface tension of its solution is 2.5 × 10^-2 N m^-1. What is the radius of the bubble?
A.
0.25 mm
B.
0.50 mm
C.
1.0 mm
D.
2.0 mm
Correct Answer:
1.0 mm
Explanation:
Using ΔP = 4T/r, the radius is r = 4T/ΔP = 4(2.5 × 10^-2)/100 = 1.0 × 10^-3 m, or 1.0 mm.
7. The surface tension of a soap solution increases from 2.5 × 10^-2 N m^-1 to 4.0 × 10^-2 N m^-1 while the bubble radius remains constant. By what factor does the excess pressure increase?
A.
0.625
B.
1.25
C.
1.60
D.
2.50
Correct Answer:
1.60
Explanation:
For fixed radius, the excess pressure ΔP = 4T/r is directly proportional to surface tension. Hence, the factor of increase is 4.0 × 10^-2 divided by 2.5 × 10^-2, which equals 1.60.
8. A soap bubble is formed inside a chamber where the external pressure is 1.00 × 10^5 Pa. If its radius is 1.0 mm and the surface tension is 2.0 × 10^-2 N m^-1, what is the pressure inside the bubble?
A.
1.0004 × 10^5 Pa
B.
1.0008 × 10^5 Pa
C.
1.0040 × 10^5 Pa
D.
1.0080 × 10^5 Pa
Correct Answer:
1.0080 × 10^5 Pa
Explanation:
The excess pressure is ΔP = 4T/r = 4(2.0 × 10^-2)/(1.0 × 10^-3) = 80 Pa. Therefore, the internal pressure is 1.00 × 10^5 + 80 = 1.0080 × 10^5 Pa.
9. Two soap bubbles of different radii are connected by a narrow tube. Ignoring other effects, in which direction does air initially flow?
A.
From the larger bubble to the smaller bubble because the larger bubble has a greater surface area
B.
From the smaller bubble to the larger bubble because the smaller bubble has greater excess pressure
C.
From the larger bubble to the smaller bubble because its curvature is smaller
D.
No air flows because both bubbles have the same surface tension
Correct Answer:
From the smaller bubble to the larger bubble because the smaller bubble has greater excess pressure
Explanation:
For soap bubbles, ΔP = 4T/r. The smaller bubble has the smaller radius and therefore the greater internal excess pressure. Air consequently flows from the smaller bubble toward the larger bubble.
10. For a hemispherical section of a soap bubble of radius r, which force balance correctly leads to the excess-pressure formula?
A.
ΔPπr^2 = 2πrT, giving ΔP = 2T/r
B.
ΔPπr^2 = 4πrT, giving ΔP = 4T/r
C.
ΔP(4πr^2) = 2πrT, giving ΔP = T/(2r)
D.
ΔP(2πr^2) = 4πrT, giving ΔP = 2T/r
Correct Answer:
ΔPπr^2 = 4πrT, giving ΔP = 4T/r
Explanation:
The excess pressure acts over the projected area πr^2. A soap bubble has two surfaces, and each contributes a surface-tension force 2πrT along the rim, so the total opposing force is 4πrT. Equating forces gives ΔPπr^2 = 4πrT and hence ΔP = 4T/r.
Short Questions and Answers
Practice short questions and answers related to
Excess Pressure in a Soap Bubble
.
Short questions are currently unavailable for this page.