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Expansion of Substances (Thermal Expansion) - Expansion of Liquids

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Topics

  • Introduction
  • Volumetric Expansion
  • Anomalous Behavior of Water

Introduction:

Liquids expand when heated because their particles move faster and spread apart, increasing their volume. Unlike solids, liquids have no definite shape but do have a definite volume. Therefore, only volumetric expansion is relevant for liquids. The amount of expansion depends on the type of liquid, its initial volume, and the temperature change. Water shows a unique behaviour, called the anomalous expansion of water, where it contracts instead of expanding between 0°C and 4°C. Liquid expansion is important in devices like thermometers and industrial systems.

Volumetric Expansion:

When a liquid is heated, its volume increases due to thermal expansion. This increase in volume depends on the initial volume (V1), the temperature change (ΔT), and the volumetric expansion coefficient (β) of the liquid.

The final volume of a liquid after heating is given by: V2 = V1(1 + βΔT)

Where:

  • V1: initial volume of the liquid.
  • V2: final volume of the liquid.
  • β: volumetric expansion coefficient of the liquid (specific to the liquid).
  • ΔT: change in temperature (T2−T1).

Volumetric Expansion Coefficient (β),

Represents the fractional change in volume per unit temperature increase.

`beta=(DeltaV) / (V_1.DeltaT) `

Unit: 1/°C.

Anomalous Behavior of Water:

Water behaves differently from most liquids when heated between 0°C and 4°C. Instead of expanding, water contracts in this temperature range. 

  • As water cools from 4°C to 0°C, its density decreases and volume increases, unlike other liquids.
  • At 4°C, water has its maximum density and minimum volume. When heated above 4°C, it behaves like other liquids and expands with temperature.

Liquid expansion has significant applications in thermometers, industry, and hydraulic systems.

 
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