Day 21 – ECET 2026 Morning Section: Expansion of Solids and Liquids

Introduction

When solids or liquids are heated, their dimensions change. This is called thermal expansion. It plays a vital role in engineering and daily life, like railway tracks, bridges, and thermometers.

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Concept Explanation

1. Expansion of Solids

When a solid is heated, its length, area, or volume increases.

• Linear Expansion

• α = coefficient of linear expansion (per °C)
• L = original length
• ΔT = temperature change

Area Expansion

• β ≈ 2\alpha

Volume Expansion

• γ ≈ 3\alpha

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2. Expansion of Liquids

Liquids expand only in volume when heated.

• Volumetric Expansion

Apparent Expansion of Liquids
Since liquid is kept in a container, we observe only apparent expansion.

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3. Important Notes

• Expansion depends on material and temperature rise.
• Gases expand much more than solids and liquids.
• Everyday uses:
  • Gaps left in railway tracks.
  • Mercury expansion in thermometers.
  • Metal lids loosen when heated.

MCQs – Practice Questions

1. Linear expansion formula is –
A)
B)
C)
D) None

2. If a rod of length 2 m, α = 1.2 × 10⁻⁵/°C, ΔT = 100°C, find ΔL –
A) 0.0024 m
B) 0.024 m
C) 0.24 m
D) 2.4 m

3. For solids, relation between coefficients is –
A) β = α, γ = 2α
B) β = 2α, γ = 3α
C) β = 3α, γ = α
D) None

4. SI unit of coefficient of linear expansion is –
A) /°C
B) J
C) N/m
D) Watt

5. Volume expansion of liquid formula is –
A)
B)
C)
D)

6. Apparent expansion of liquid formula is –
A)
B)
C)
D) None

7. Which expands least on heating?
A) Solids
B) Liquids
C) Gases
D) All equal

8. When mercury is heated in a glass bulb, observed expansion is –
A) True expansion
B) Apparent expansion
C) No expansion
D) Negative expansion

9. Railway track gaps are left due to –
A) Electrical effect
B) Thermal expansion
C) Friction
D) Elasticity

10. Unit of coefficient of volume expansion is –
A) /°C
B) J
C) N
D) Pascal

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Answer Key

1. A
2. A
3. B
4. A
5. C
6. B
7. A
8. B
9. B
10. A

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Explanation

• Q1 → Linear expansion formula.
• Q2 → ΔL = α L ΔT = 1.2×10⁻⁵ × 2 × 100 = 0.0024 m → Option A.
• Q3 → Relation: β = 2α, γ = 3α.
• Q4 → Unit of α is per °C.
• Q5 → For liquids, ΔV = γ V ΔT.
• Q6 → Apparent expansion = liquid – container.
• Q7 → Solids expand least.
• Q8 → Observed = apparent expansion.
• Q9 → Due to thermal expansion.
• Q10 → γ unit = per °C.