chemistry : class11 Capillary Rise : Surface tension : States of Matter: Gases and Liquids MCQ Questions and Answers
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Capillary Rise
MCQ questions and answers.
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MCQ Questions
1. What is meant by capillary rise?
A.
The rise of a liquid in a narrow tube due to surface tension
B.
The sinking of a liquid in a wide vessel due to gravity
C.
The evaporation of a liquid from its surface
D.
The expansion of a liquid on heating
Correct Answer:
The rise of a liquid in a narrow tube due to surface tension
Explanation:
Capillary rise is the upward movement of a liquid in a narrow tube caused mainly by surface tension and adhesive forces between the liquid and the tube.
2. In a capillary tube, water rises because its adhesive force with glass is:
A.
Greater than the cohesive force within water
B.
Less than the cohesive force within water
C.
Equal to the gravitational force only
D.
Zero at the liquid surface
Correct Answer:
Greater than the cohesive force within water
Explanation:
Water wets glass because the adhesive force between water and glass is greater than the cohesive force among water molecules, causing water to rise in the capillary.
3. If the radius of a capillary tube is decreased, the height of liquid rise in it will:
A.
Increase
B.
Decrease
C.
Remain unchanged
D.
Become zero
Correct Answer:
Increase
Explanation:
The height of capillary rise is inversely proportional to the radius of the capillary tube, so a narrower tube produces a greater rise.
4. Which formula represents the capillary rise of a liquid in a narrow tube?
A.
h = 2T cos θ / (rρg)
B.
h = rρg / (2T cos θ)
C.
h = 2rρg / (T cos θ)
D.
h = T rρg cos θ
Correct Answer:
h = 2T cos θ / (rρg)
Explanation:
The capillary rise is given by h = 2T cos θ / (rρg), where T is surface tension, θ is the contact angle, r is tube radius, ρ is density, and g is acceleration due to gravity.
5. For a liquid that completely wets the wall of a capillary tube, the contact angle is approximately:
A.
0°
B.
45°
C.
90°
D.
180°
Correct Answer:
0°
Explanation:
A liquid that completely wets the tube has a contact angle close to 0°, making cos θ equal to 1 and producing maximum capillary rise for given conditions.
6. What happens to the capillary rise of water if the same capillary tube is used on the Moon, ignoring changes in surface tension and density?
A.
It increases
B.
It decreases
C.
It remains exactly the same
D.
It becomes negative
Correct Answer:
It increases
Explanation:
Capillary rise is inversely proportional to gravitational acceleration. Since gravity is lower on the Moon, the height of water rise increases.
7. A liquid rises in a capillary tube when the contact angle is:
A.
Less than 90°
B.
Exactly 180°
C.
Greater than 180°
D.
Always exactly 90°
Correct Answer:
Less than 90°
Explanation:
When the contact angle is less than 90°, cos θ is positive, so the liquid rises in the capillary tube.
8. If the surface tension of a liquid increases while other factors remain constant, its capillary rise will:
A.
Increase
B.
Decrease
C.
Remain unchanged
D.
Become zero
Correct Answer:
Increase
Explanation:
The capillary rise is directly proportional to surface tension, so increasing surface tension increases the height of rise.
9. Which liquid generally shows a depression in a glass capillary tube?
A.
Mercury
B.
Water
C.
Alcohol
D.
Kerosene
Correct Answer:
Mercury
Explanation:
Mercury does not wet glass because its cohesive forces are stronger than its adhesive forces with glass, so its level is depressed in a capillary tube.
10. Two capillary tubes have radii 1 mm and 2 mm. For the same liquid and conditions, the liquid rises higher in the tube of radius:
A.
1 mm
B.
2 mm
C.
Both tubes equally
D.
Neither tube
Correct Answer:
1 mm
Explanation:
Since capillary rise is inversely proportional to tube radius, the tube with radius 1 mm gives twice the rise compared with the tube of radius 2 mm.
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