🌡️ INTRODUCTION

Thermal Expansion is the phenomenon in which the dimensions of a material change when its temperature changes. When a substance is heated, its particles gain kinetic energy, move more vigorously, and increase the distance between them, leading to expansion. On cooling, the substance contracts.

This chapter explains different types of expansion such as linear, area, and volume expansion, along with their coefficients. It also covers practical applications and exceptions like anomalous expansion of water.

Thermal expansion is important for competitive exams because it involves both conceptual understanding and numerical problems based on formulas and real-life applications.

⚡ Quick Revision Notes (Complete Chapter)

🔥 Thermal Expansion:
Increase in length, area, or volume due to rise in temperature

📏 Types of Expansion:

• Linear Expansion (length)

• Area Expansion (surface)

• Volume Expansion (bulk)

📐 Linear Expansion:
Change in length ∝ original length × temperature change

📊 Coefficient of Linear Expansion (α):
α = (ΔL) / (L × ΔT)

📦 Volume Expansion:
Change in volume ∝ original volume × temperature change

📊 Coefficient of Volume Expansion (γ):
γ = (ΔV) / (V × ΔT)

🔗 Relation Between Coefficients:
γ = 3α (for isotropic solids)

🌊 Expansion of Liquids:
Liquids expand more than solids
Real expansion vs apparent expansion

💨 Expansion of Gases:
Gases expand the most
Follows gas laws (Charles’ law)

❄️ Anomalous Expansion of Water:
Water contracts from 0°C to 4°C and expands above 4°C
Maximum density at 4°C

⚙️ Practical Applications:

• Railway tracks gaps

• Expansion joints in bridges

• Thermometers

• Bimetallic strips

⚠️ Bimetallic Strip:
Two metals with different expansion coefficients bend on heating

📌 Key Concept:
Expansion depends on material, temperature change, and initial dimensions