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Thermal Properties Of Matter

Thermal expansion : applications and consequences

Physics

Thermal expansion of solids is useful in some situations of daily life and in some situations it creates problems:

APPLICATIONS:

Bimetallic thermostat

Bimetallic thermostat is used to control temperature of ovens, irons, water heaters, refrigerators, air conditioners and so on.

It is designed to bend when it becomes hot. Two metals with different coefficient of linear expansion are joined firmly to make it . When it is heated, metal with the value of coefficient of linear expansion expands more causing the the strip to bend. In this way, it cuts off the current supply. The current supply to the circuit is restored again when it cools down.

Rivets

Rivets are used in shipbuilding and other industries to join metal plates. A red-hot rivet is passed through holes in two metal plates and hammered until ends are rounded. The rivet contracts on cooling and pulls the two plates tightly together.

Fixing a Metal Rim on a Wooden Wheel

A metal rim can be fixed on a wooden wheel of a bull cart. The diameter of metal rim is set little bit smaller than the diameter of wooden wheel. The diameter of metal rim increases on heating and can easily be put over the wooden wheel. It contracts on

cooling and holds wooden wheel tightly

Mercury in Thermometer

Mercury expands on heating and contracts on cooling. It do not stick to the walls of thermometer. Therefore Mercury is placed in long sealed capillary tube in thermometer. Change in the temperature is measured by the position of mercury in capillary tube which has calibrated marks with °C\degree C , °F\degree F or KK scale.

CONSEQUENCES:

Rail Tracks

The rail tracks are made up of metals and hence they expand in summer due to hot weather. Hence, small gaps are left at the joints of sections of tracks this allows the tracks to expand safely. If these gaps are not left between the tracks, the tracks buckled and train would be de-tracked (derailed).

Car Radiator Coolant

Engine coolant is used in car radiator in place of pure water because water has greater volume expansion it can expand enough to damage the engine or radiator.