Class 9 > Unit # 09:Thermal Properties of Matter > Applications of Thermal Expansion

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Applications of Thermal Expansion in Daily Life

Q. Describe applications of thermal expansion in our daily lives.

Thermal expansion plays a critical role in engineering designs, industrial processes, and everyday household devices. Below are the key applications:

1. Bimetallic Thermostat:

   A bimetallic thermostat is used to control the temperature of ovens, irons, water heaters, refrigerators, and air conditioners. It is constructed by joining two different metals with unequal coefficients of linear expansion firmly together. When heated, the metal with the larger coefficient of linear expansion expands more than the other, causing the strip to bend and cut off the electrical current supply. Upon cooling, it straightens and restores the circuit connection.

2. Rivets and Metal Rims:

   Rivets are used in shipbuilding and structural industries to join metal plates securely. A red-hot rivet is inserted through aligned holes in metal plates and hammered until its ends are flattened. Upon cooling, the rivet contracts powerfully, pulling the two plates tightly together. Similarly, a metal rim with a diameter slightly smaller than a wooden cart wheel is heated so its diameter expands, allowing it to slip easily over the wheel. On cooling, it contracts and grips the wheel tightly.

3. Car Radiator Coolant:

   Engine coolant is used in car radiators instead of pure water because water has a high volume expansion coefficient and distinct anomalous expansion properties that could expand excessively and damage the engine block or radiator core under extreme thermal stresses.

4. Mercury in Thermometers:

   Mercury expands uniformly upon heating and contracts upon cooling without sticking to the inner glass walls of the capillary tube. Because of this reliable thermal expansion, mercury is sealed inside long capillary tubes with calibrated temperature scales ($^\circ\text{C}$, $^\circ\text{F}$, or $\text{K}$) to measure temperature changes accurately.

5. Rail Tracks:

   Rail tracks are made of steel and expand significantly during hot summer weather. To prevent buckling and subsequent train derailments, small expansion gaps are intentionally left between successive sections of the rail tracks to allow safe linear expansion.

Fig: Practical engineering applications showing a bending bimetallic strip and rail track expansion joints.

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