Consider the following statements: If there were no phenomenon of capillarity 1. It would be difficult to use a kerosene lamp 2. One would not be able to use a straw to consumer a soft drink 3. The blotting paper would fail to function 4. The big trees that we see around would not have grown on the Earth Which of the statements given above are correct?
Contents15
- A1, 2 and 3 only
- B1, 3 and 4 only
- C2 and 4 only
- D1, 2, 3 and 4
Show answer
Answer: (B) 1, 3 and 4 only
Without capillarity:
Statement 1 correct — kerosene lamps rely on capillary action to draw fuel up through the wick.
No capillarity = no fuel rising = lamp won't work.
Statement 3 correct — blotting paper absorbs ink through capillary action in its tiny pores.
No capillarity = no absorption.
Statement 4 correct — tall trees transport water from roots to leaves partly through capillary action in xylem vessels (along with transpiration pull and root pressure).
No capillarity = water can't reach treetops.
Statement 2 is WRONG — drinking through a straw works by AIR PRESSURE DIFFERENCE, not capillarity.
When you suck, you reduce air pressure inside the straw, and atmospheric pressure pushes the liquid up.
Answer: 1, 3 and 4 only.
Capillary action enables water and other liquids to move upward against gravity through narrow spaces, making it essential for kerosene lamps, blotting paper absorption, and water transport in tall trees.
The key trap is confusing air pressure mechanisms with capillary action - drinking through a straw uses atmospheric pressure difference when you create suction, not capillarity.
This tests whether students can distinguish between different physical mechanisms that move liquids upward in everyday applications.
Capillary Action Mechanism
Science And Technology capillarity capillary action
Capillary Action: Mechanism & Physics
Capillary action is liquid rising or falling in narrow tubes due to surface tension
Works through adhesion (liquid-solid attraction) and cohesion (liquid-liquid attraction)
Height of rise is inversely proportional to tube diameter
Water rises in glass tubes but mercury falls due to different adhesive forces
What Causes Capillarity
Capillary action occurs when liquid molecules are more attracted to the container walls than to each other. This creates surface tension forces that pull the liquid up narrow spaces against gravity.
Adhesion: attraction between liquid and solid (water to glass)
Cohesion: attraction between liquid molecules (water to water)
When adhesion > cohesion → liquid rises (water in glass)
When cohesion > adhesion → liquid depresses (mercury in glass)
How Capillarity Works
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flowchart TD
s1["`**Liquid touches narrow tube/pore**
Surface molecules experience unequal forces`"]
s2["`**Adhesive forces dominate**
Liquid molecules attracted more to tube walls than each other`"]
s3["`**Meniscus forms**
Curved liquid surface creates pressure difference`"]
s4["`**Liquid rises**
Surface tension pulls liquid column upward until balanced by weight`"]
s1 --> s2
s2 --> s3
s3 --> s4Trap: Straws work by air pressure difference, NOT capillarity
Trap: Capillary height is inversely proportional to tube diameter — thinner tubes = higher rise
Trap: Mercury depresses in glass capillaries while water rises
Kerosene Lamp Functioning
Science And Technology kerosene lamp
Kerosene Lamps: Capillary-Based Fuel Transport
Kerosene lamps use cotton wicks to transport fuel from reservoir to flame
Wick fibers act as capillary tubes drawing kerosene upward against gravity
Without capillarity, kerosene stays in bottom reservoir and flame dies
Why Capillarity is Essential
A kerosene lamp's cotton wick contains thousands of tiny fibers that create narrow spaces between them. These spaces act as capillary tubes that continuously draw kerosene from the bottom reservoir to the top where it burns.
Kerosene Transport Process
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flowchart TD
s1["`**Wick dips into kerosene**
Bottom end stays submerged in fuel reservoir`"]
s2["`**Capillary action starts**
Kerosene rises through fiber spaces due to adhesion`"]
s3["`**Fuel reaches flame zone**
Continuous upward flow maintains fuel supply`"]
s4["`**Combustion occurs**
Heat vaporizes kerosene at wick tip for burning`"]
s1 --> s2
s2 --> s3
s3 --> s4Statement 1 is CORRECT — kerosene lamps depend entirely on capillary action
Trap: Don't confuse with modern pressure lamps that use different mechanisms
Drinking Straw Mechanism
Science And Technology straw
Drinking Straws: Air Pressure, NOT Capillarity
Straws work by atmospheric pressure difference, NOT capillary action
Sucking creates partial vacuum inside straw
Atmospheric pressure (15 psi) pushes liquid up into low-pressure straw
Capillary effect in straws is negligible — only raises liquid few millimeters
The Real Physics
When you suck on a straw, you remove air and create lower pressure inside. Atmospheric pressure (about 15 pounds per square inch) acting on the drink surface becomes greater than the pressure inside the straw, pushing the liquid up.
How Straws Actually Work
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flowchart TD
s1["`**Normal state**
Equal air pressure inside straw and outside`"]
s2["`**Sucking begins**
Mouth removes air from straw, creating partial vacuum`"]
s3["`**Pressure difference**
Atmospheric pressure > straw pressure`"]
s4["`**Liquid rises**
Higher outside pressure pushes liquid up into straw`"]
s1 --> s2
s2 --> s3
s3 --> s4Statement 2 is WRONG — this is the KEY trap in the question
Trap: Students confuse 'liquid rising in tube' with capillary action
Proof: Straws work even with wide diameter — capillarity needs narrow spaces
Blotting Paper Absorption
Science And Technology blotting paper
Blotting Paper: Capillary Absorption System
Blotting paper has millions of tiny pores between cellulose fibers
These pores act as capillary tubes that suck up ink/liquid
Without capillarity, ink would just sit on surface without absorption
Microscopic Structure
Blotting paper is made from loosely woven cellulose fibers that create countless microscopic spaces. These tiny pores range from 10-100 micrometers and function as a network of capillary tubes.
Ink Absorption Process
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flowchart TD
s1["`**Ink contacts paper**
Liquid touches pore openings on paper surface`"]
s2["`**Capillary forces activate**
Adhesion between ink and cellulose fibers`"]
s3["`**Ink drawn inward**
Liquid spreads through pore network by capillarity`"]
s4["`**Paper absorbs ink**
Ink distributed throughout paper thickness`"]
s1 --> s2
s2 --> s3
s3 --> s4Statement 3 is CORRECT — blotting paper entirely depends on capillary action
Trap: Don't confuse with regular paper — blotting paper has special porous structure
Water Transport in Trees
Science And Technology big trees
Water Transport in Tall Trees: Multiple Mechanisms
Trees use three mechanisms to transport water: capillarity, transpiration pull, root pressure
Xylem vessels act as capillary tubes — typically 20-200 micrometers wide
Transpiration pull is the main force for reaching 30+ meter heights
Capillary action alone can lift water 1-2 meters — crucial for initial uptake
Why Capillarity Matters
While transpiration pull is the primary mechanism for tall trees, capillary action in xylem vessels is essential for the initial water uptake and maintaining continuous water columns. Without capillarity, water transport would fail at the microscopic level.
Water Transport Mechanisms
Mechanism | Maximum Height | How It Works | Role in Trees |
|---|---|---|---|
Capillary Action | 1-2 meters | Surface tension in narrow xylem vessels | Initial uptake, maintains water columns |
Transpiration Pull | 100+ meters | Negative pressure from leaf water loss | Main force for tall trees |
Root Pressure | Few meters | Active ion pumping creates pressure | Pushes water up, especially at night |
Statement 4 is CORRECT — capillarity is essential for water transport in trees
Trap: Students think only transpiration matters — capillarity is equally crucial
Trap: Without capillary action, water columns in xylem would break and fail