6.0 THERMAL EXPANSION

Thermal expansion is the tendency of matter to change its shape, area, and volume in response to a change in temperature. When substances are heated, their particles gain kinetic energy and vibrate more vigorously. This increased vibration causes them to take up more space, so the material expands. This chapter explores how solids, liquids, and gases expand, with special attention to the unusual behavior of water and its profound biological importance.

6.1 Expansion in Solids

When a solid is heated, the particles vibrate more about their fixed positions. They need more room to move, so the overall dimensions of the solid increase. Different solids expand at different rates.

6.1.1 Linear Expansion

Linear expansion refers to the increase in length of a solid when heated. The amount of expansion depends on:

• The original length (longer objects expand more in absolute terms).
• The temperature change (greater temperature difference → more expansion).
• The material – each material has a characteristic coefficient of linear expansion (α).

Example calculation idea: A metal rod of length L₀ heated by ΔT expands by ΔL = α L₀ ΔT. For steel, α is about 0.000012 /°C.

6.1.2 The Bimetallic Strip

A bimetallic strip is made by joining two different metals (e.g., brass and iron) tightly together. Brass expands more than iron for the same temperature rise.

• When heated

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